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FIRST BOOK IN ASTRONOMY, ' 



ADAPTED TO THE 



USE OF COMMON SCHOOLS 



LLUSTRATED WITH STEEL PLATE ENGRAVINGS. 





BY REV. J. L. BLAKE. A. M. 



AUTHOR OF THE HISTORICAL READER, IMPROVEMENTS IN BLAKe's 
NATURAL PHILOSOPHY, BIBLICAL READER, GEOGRAPHY FOR 
CHILDREN, AND OTHER WORKS ON EDUCATION. 



" All Nature is a glass reflecting God, 
As by the sea reflected is the sun, 
Too glorious to be gaz'd on in his sphere." 



BOSTON: 
LINCOLN AND EDMANDS 



~^-v.. 



Portland, S. Colman .- Hartford, Packard & Butler : New-York, Roe Lock- 
wood : Philadelphia, L. A. Key : Baltimore, Joseph Jewett : Charleston, 
J. J. M'Carter : Cincinnati, N. & G. Guilford. 

1831. 




DISTRICT OF MASSACHUSETTS, to icit : 

District Clerk's Office. 
BE IT REMEMBERED, That on the twenty-third day of February, A. D 
1831, in the fifty-fifth year of the Independence of the United States of Amer 
ica, Lincoln & Edmands, of the said district, have deposited in this office 
the title of a Book, the right whereof they claims as proprietors, in tLe 
words following, to tcit : 

" First Book in Astronomy, adapted to the Use of Common Schools. Il- 
lustrated with Steel Plate Engravings. By J. L. Blake, A. M. Author of 
the Historical Reader, Improvements in Blake's Natural Philosophy, Biblical 
Reader, Geography for Children, and other Works on Education. 
*' ' All Nature is a glass reflecting God, 
As by the sea reflected is the sun. 
Too glorious to be gaz'd on in his sphere.' " 
In Conformity to the Act of the Congress of tlie United States, entitled, 
" An Act for the encouragem^ent of Learning, by securing the copies of Maps, 
Charts, and Books, to the Authors and Proprietors of such copies during the 
times therein mentioned ;" and also to an Act entitled " An Act supplemen- 
tary to an Act, entitled An Act for the Encouragement of Learning, by se- 
curing the Copies of Maps, Charts, and Books to the Authors and Propri- 
etors of such Copies during the times therein mentioned : and extending 
the Benefits thereof to the' Arts of Designing, Engraving and Etching His- 
torical, and other Prints." 

JNO. W. DAVIS, Clerk of the District of Massachusetts. 



r^/^ 



PREFACE 



Two objects are to be continually kept in view by every pergon engaged 
in communicating literary and scientific knowledge. One of these objects 
is, to make a judicious selection of topics ; and the other is, to present them 
in a form most likely to interest the attention, and thereby produce distinct 
and deep impressions on the understanding and the memory. These objects 
are too much neglected both by teachers and the authors of elementary works 
on education. A teacher may possess an abundance of erudition in the 
branches to be taught; but completely fail in rendering his instructions of 
much value to his pupils by an inattention to the particulars named. And 
a book, on elementary education, may excel in the accuracy of its details, as 
well as in relation to the ability with which the general plan is executed; 
but still be most defective in answering the purpose for which it was designed. 
To answer the purpose contemplated in such a work, it must be suited to the 
taste and the mental capacity of the persons to be benefitted by it. 

It sometimes happens, and not very unfrequently, that an author will 
crowd into a book, whether needed or not, everything he knows on the sub- 
ject of which it treats. Hence, we see in school books for the use of quite 
young scholars, matters altogether above their comprehension. The evil 
arising from such instances of ostentation is far more extensive than at first 
imagined. It is not simply a waste of space occupied by the irrelevant mat- 
ters alluded to ; but, if scholars find one half of a book above their compre- 
hension, they will be likely to throw aside the whole of it in disgust. A 
teacher also may be influenced by a similar desire to excite admiration, and 
adopt similar means for securing it. Accordingly, he will bring into school, 
for the use of mere boys and girls, books which are suited to the highest 
grade of students in college ; but which his ov/n scholars will understand 
about as well as they would the entire system of Egyptian hieroglyphics. 
Place before young scholars one book, and another, and another, which they 
cannot understand, and they will be likely to have an aversion to every- 
thing in the form of books. 

To produce the best possible eff'ects from the use of books, they should 
contain nothing that children of ordinary capacity, with proper instruction, 
are unable to comprehend. They should also be filled with what is enticing 
in its appearance. The very form in which things suitable for young persons 
are presented,' should be pleasing to the eye. Hence, long paragraphs, long 
articles on the same subject, a long succession of pages filled precisely in the 



IV fREFACE. 

manner, presenting an aspect as dull and monotonous, as a sand desert with- 
out variation or limits, are alike unfavorable in their effects on the interests 
of education. 

It is proper to remark, that the author has attempted to prepare the follow- 
ing little work in accordance with the foregoing suggestions. How far he 
has been successful in making this attempt teachers and the public general- 
ly will determine. Whatever is abstruse, and difficult, and suited only for 
the highest class of learners, has been carefully excluded. To supply the 
place of what is thus excluded, there is introduced a mass of miscellaneous 
matter, on a level with the mental perceptions of those for whose improve- 
ment and gratification the volume is prepared. Meteorology is nearly allied 
to Astronomy, and is in a high degree interesting. A small volume on this 
subject might be furnished, in every respect calculated to excite a taste in 
young persons for literary pursuits. 

No subject is more imposing and sublime than Astronomy. No one is bet- 
ter calculated to gain the attention of children ; and to raise in the mind a 
highly improved state of moral sentiment, and moral feeling. The poet 
truly said, " an undevout astronomer is mad." Intellectual and moral disci- 
pline should always be united, in pursuing a course of education. For such 
an union of beneficial results, we may rationally look in presenting to the 
youth of our country, the present brief compend. And the more effectually 
to aid in the accomplishment of a purpose so desirable, may teachers and 
pupils ever be enabled piously to unite in the following aspiration : 

" Astronomy ! Parent of Devotion, engage my midnight vigils 5 
Elevate my thought to contemplate thy vast realities ; 
Warm my soul with adoration pure, and fervent praise 
To HIM, whose finger fashioned yon revolving worlds." 



FIRST BOOK IN ASTRONOMY 



ASTRONOMICAL AND GEOMETRICAL DEFINITIONS. 

LESSON I. 

The Definitions here given are in as few words as possible, with a view 
to their being committed to memory. Each one may be considered an an- 
swer to a distinct question, which the teacher should propose at the time of 
reciting. For instance, What is astronomy ? What is a circle .' What is a 
planet .? &c. If this lesson is too long to be recited at one time, it can easily 
be divided into two or more lessons. 

Astronomy is the science which describes the heavenly bodies ; 
the Sun, Planets, Fixed Stars, and Comets. 

A planet is an opaque, or dark body, deriving its light from an- 
other body, around which it revolves. 

A comet is a body which moves round the sun in a very eccentric 
orbit or tract, and is usually accompanied with a long train of light. 

The orhit of any celestial body is the curve or path it describes 
in revolving round another body. 

Two celestial bodies are said to be in opposition^ when they are 
in opposite points of the heavens. 

Two celestial bodies are said to be in coiyunction, when they are 
in the same point of the heavens. 

A planet is said to move direct, when it appears to move accord- 
ing to the signs of the ecliptic. 

A planet is said to move retrograde, when it appears to move 
contrary to the signs of the ecliptic. 

A planet is said to be stationary, when it appears to remain any 
particular time in a certain point of the heavens. 

A circle is a plane figure bounded by a curved line, called the cir- 
cumference, every part of which is equally distant from the centre. 



6 FIRST BOOK IN ASTRONOMY. 

The diameter of a circle is a line drawn through the centre, ter- 
minated both ways by the circumference. 

The radius of a circle is a straight line drawn, in either direc- 
tion, from the centre to the circumference. 

A semicircle is any half of a circle, or circumference, cut off from 
the other half by the diameter. 

A quadrant is half a semicircle, or circumference ; or it is one 
fourth part of a whole circle. 

All circles^ whether great or small, are supposed to be divided 
into 360 equal parts, called degrees, and are marked °. 

Each degree is divided into sixty minutes, marked ' ; and each 
minute is divided into sixty seconds, marked ". 

An arc of a circle is any portion of tlie circumference, less than 
one half, or less than a semicircle. 

The chord of a circle is a straight line joining together the ex- 
tremities of an arc. 

An angle is the space contained between two lines meeting in a 
point. 

A right angle is an angle formed by one line falling perpendicu- 
lar upon another line, containing ninety degrees, or the quadrant 
of a circle. 

An obtuse angle is greater than a right angle ; containing more 
than the quadrant of a circle, or ninety degrees. 

An acute angle is less than a right angle ; containing less than 
ninety degrees, or the quadrant of a circle. 

Parallel lines, whether straight or circular, are everywhere at 
the same distance from each other ; and, if drawn ever so far 
either way, will never meet. 

A sphere is properly a globe ; but, in astronomy, the celestial 
sphere means the apparently concave orb of the heavens, in which 
all the heavenly bodies appear to be placed. 

Concentric circles are circles drawn round the same centre, at 
different distances from it. 

Cardinal points are certain fixed points that never change, and 
to which all calculations are referred. 

An ellipsis is an oval. This figure differs from a circle, in being 
unequal in its diameters, and in having two points called its foci. 

The foci are the two points in the longest axis of an ellipsis, on 
which as centres the figure is described. 

The eccentricity of an ellipsis is the distance between the centre 
and either foci. . 



PL^TEU 




O. I^&lton>So.. 



FIRST BOOK IN ASTRONOMY. 



ILLUSTRATION OF GEOMETRICAL DEFINITIONS. 



LESSON II. 

The following Questions are to be answered from the figures in Plate II, 
being an illustration of the Geometrical Definitions. It will be well for 
the Instructer to add other similar questions, till the pupil becomes perfectly 
familiar with the matters they are intended to explain. 



1. Which figure represents a circle ? 

2. By what is the centre of it repre- 

sented .'' 

3. By what is the diameter repre- 

sented .? 

4. What part of that circle makes an 

arc 1 

5. By what is the chord of that arc 

represented ? 

6. By what line is the circle divided 

into semicircles .'' 

7. Which figure exhibits a right an- 

gle .? 

8. Why is that figure a right angle .? 

9. Which figure exhibits an obtuse 

angle .'' 

10. Why is that an obtuse angle ? 

11. Which figure represents an acute 
angle .? 

12. Why is that figure an acute angle .? 

13. By which figure are concentric 
circles represented? 

14. Which two figures represent par- 
allel lines .' 

15. Which figure contains six parallel 
lines ^ 



IG. What two lines in fig. 1, are par- 
allel .? 

17. By which figure is an ellipsis rep- 
resented .' 

18. By what are the foci of it repre- 
sented ? 

19. What is the eccentricity of this 
ellipsis.'' 

20. Which figure represents a semi- 
circle i 

21. How many right angles does it 
contain ? 

22. What lines are the radii of the 
circle in the first figure ? 

23. How might fig. 4, be made into a 
right angle .-' 

24. How can a right angle be made 
of figure 6 .'' 

25. How can an acute angle be made 
in it .? 

26. In fig. 7, which line is the chord 

of the arc .-^ 

27. Which dotted lines in Plate II, 
are arcs of circles .'' 

28. Which dotted lines are radii of 
circles ? 



GENERAL VIEW OF THE CELESTIAL BODIES. 

LESSON III. 

When we direct our eyes towards the heavens, we perceive an 
apparent hollow hemisphere, at an infinite distance, of which each 
spectator seems to constitute the centre. The earth stretches like 
an immense plane, and at a certain distance appears to meet and 
to bound the celestial concavity. 

1. What do we observe on directing our eyes towards the heavens.' 

2. What makes the centre ? 



8 FIRST BOOK IN ASTRONOMY. 

The moBt obvious celestial phenomena are the daily rising of the 
sun in the east, and its setting in the west; next to which we also 
see the 7}io()}i and stars rise and set in like manner, keeping the 
same westerly course. 

These cannot be long observed, before we perceive that neither 
the sun nor the moon always rise exactly in the same point of the 
horizon, nor ascend to the same height. 

If, in these northern paris of the world, we observe the sun from 
the beginning of the year, it will be found to rise daily more north- 
ward, to continue longer above the horizon, and to be more elevated 
at mid-day, till near the end of June, when it will be observed to 
move backwards in like manner, till near the end of the year. 

When the Jiew moon first becomes visible, it appears in the west- 
ern part of the heavens, not far from the setting sun. Every night 
it increases in size, and removes to a greater distance from the set- 
ting sun ; till at last it appears in the east part of the horizon, just 
at the time the sun disappears in the west. 

In an unclouded evening the hemisphere is seen studded with 
stars, and its appearance is changing every instant. New stars are 
continually ascending in the east, while others are descending in 
the west. 

Those stars, that towards the beginning of the evening were just 
visible in the east, are seen late at night over our heads, and may 
be traced moving gradually westward, till at last they disappear al- 
together. 

If we look to the north, we may perceive that many stars in that 
quarter never set at ail, but move round, describing a complete cir- 
cle in every twenty-four hours. 

These stars will be found to describe their circles round a fixed 
point of the heavens, near which is a star of the second magni- 
tude, called the north or pole star. 

Thus the heavenly sphere appears to turn round two fixed points, 
called the poles, once every twenty-four hours. The imaginary 
line which joins these points is called the axis of the world. 



3. What are the most obvious celestial phenomena? 4. And of the moon 

and stars ?■ 5. Do the sun and moon always rise in the same point of the 

horizon? 6. How do they vary? 7. Wheie does the new moon first 

become visible? 8. What change in its place and size takes place every 

night? y. Whut is said of the stars in an unclouded evening? 

10. Where will those be seen late at night, which at the beginning of the 
evening, were seen just above the horizon ? 11. Afterwards what is ob- 
served of them ? 12. If we look to the north, what may be observed of 

the movement of the stars ? 13. Round what do they describe their circle ? 

14. Around what does the heavenly sphere appear to revolve ? 15. How 

often does it thus appear to revolve ? 16. By what are these two points 

connected ? 



FIRST BOOK IN ASTRONOMY. « 

The chief part of the stars keep their places with respect to each 
other. Thus, if two stars have a certain apparent distance from 
each other on one night, they keep the same distance every night, 
and are called jixed stars. 

But some of the stars are not of this fixed kind. They change 
their places, as well with regard to the fixed stars, as to one an- 
other. These are called planets. 



DIFFERENT SYSTEMS OF ASTRONOMY. 

LESSON IV. 

It is natural to conclude, that the beauty and the continually 
varying appearance of the heavenly bodies, at an early period of 
the world, became objects of scientific inquiry and of religious 
contemplation. To this the pastoral life, when persons were em- 
ployed by night in watching their flocks, was particularly favorable. 

Accordingly it is found, that within a few centuries of the del- 
uge, Astronomy was cultivated in China, in Hindostan, at Nineveh, 
at Babylon, and in Egypt. The Phoenicians are said to have ap- 
plied it to the purposes of navigation, but we have no reason to be- 
lieve it was reduced to a regular science till the time of Pythagoras. 

The present system of astronomy was first taught by Pythagoras, 
590 years before the Christian era ; but it was afterwards rejected, 
until the sixteenth century, when it was revived by Copernicus, a 
native of Poland, from whom it is called, the Copernican system. 

Thales, a celebrated philosopher of Miletus, was the first person 
who advanced the opinion that the earth is round, and that the 
moon is the attendant of the earth, both deriving their light and 
heat from the sun. He also supposed that the eclipses of the moon 
are occasioned by an immersion in the earth's shadow. 



16. What are called jfixed stars ? 17. Are all the stars in the heavens fixed 

stars ? 18. What ones are called planets ? 

1. What situations in the early ages of the world were favorable to the 

study of Astronomy.? 2. At what places, was it at first cultivated ? 

3. How soon was it there cultivated ? 4. At what time, and by whom, was 

the science of astronomy first reduced to a regular system ? 5. By whom 

was first taught the present system of Astronomy .'' C. Who was Coperni- 
cus ? 7. Who was Thales ? 8. What did he teach ? 9. What did he 

suppose respecting eclipses .' 

B 



10 FIRST BOOK IN ASTRONOMY. 

Such was the ignorance and superstition of the age in which 
Pythagoras lived, that he was obliged to give his instructions in 
private ; and his disciples became the victims of religious and po- 
litical persecution. Many of them were imprisoned and compelled 
to recant their faith ; others were banished from their country, and 
some even suffered death. 

The pagan priests were the chief instruments in causing his 
opinions to be thus rejected. They taught the people to believe 
that the earth was a level plane of great extent ; that heaven was 
another of like dimensions, stretched out a little beyond the sun; 
and that hell consisted of a third plane of similar extent, situated 
at some distance below the earth. These and other notions which 
they held, had been artfully interwoven into their religion, and into 
all their political institutions, so that any innovation was not only 
treason against the state, but a species of profanity, which incurred 
the indignation of the multitude. 

Ptolemy, the Egyptian astronomer, lived one hundred and thirty 
years before Christ. He supposed the earth to be at rest in the 
centre, around which moved the sun and the planets, once a day 
in the following order; the Moon, Mercury, Venus, the Sun, Jupi- 
ter and Saturn. Beyond these were placed the fixed stars. His 
system is called the Ptolemaic system. See Plate VI. Fig. 6, 

From the time of Ptolemy, astronomy was much neglected, un- 
til near the close of the thirteenth century, when Alphonso, King 
of Castile, revived the- subject. Still no essential change in the sci- 
ence was effected, until Copernicus, in the sixteenth century, em- 
braced and published to the world the system of Pythagoras. 

Nicolas Copernicus was a native of Poland. A printed copy of 
his work was handed him but a few hours before his death. As 
he was considered the inventor, the system has been called after 
his name — the Copernican system. 

Europe, however, was still immersed in ignorance, and the gen- 
eral ideas of the world were not able to keep pace with those of a 

10. What is said of the age in which Pythagoras lived ?■ 11. What is 

said of his disciples ?• 12. Who were the chief instruments in causing his 

opinions to be rejected ? 13. What was the system of astronomy taught 

by the pagan priests ? 14. How was innovation upon their system consid 

ered? 15. When did Ptolemy,the Egyptian astronomer-live.? 16. What 

was his system.? 17. What figure illustrates his system.? 18. What 

was the state of astronomical science, subsequent to the time of Ptolemy ? 

19. Who next to him revived the study? 20. When.? 21. Who was 

Nicolas Copernicus .? 22. At what time did he flourish .? 23. What did 

he do for the science of astronomy .? 24. Why is the present system of 

astronomy called the Copernican system ? 25. What was the intellectual 

condition of Europe at the time of Copernicus .? 



FIRST BOOK IN ASTRONOMY. 11 

refined philosopher. This caused Copernicus to have few abettors 
and many opponents. 

About the same time, Tycho Brahe, a Danish nobleman, anxious 
to reconcile the appearances of nature with the literal sense of 
some passages of Scripture, adopted portions of the Ptolemaic sys- 
tem, while in other respects, he made his views conformable to the 
principles of modern astronomy. 

The projected system of Tycho was this ; in the centre of it 
he placed the earth, with the sun and moon moving round it as 
their centre; while Mercury, Venus, Mars, Jupiter, and Saturn 
revolve round the sun, and are carried with it about the earth. 

In the sixteenth century lived the celebrated astronomer Galileo, 
an Italian. He was the first who applied the telescope to the ex- 
amination of the heavens. This enabled him to make discoveries 
in the science, of which all his predecessors were utterly ignorant. 

Galileo was the victim of the persecuting spirit, which prevailed 
at that age of ignorance and superstition. When passed the age 
of three score and ten years, he was obliged by the priests, stand- 
ing upon his knees, over the Bible, to disclaim belief in a system to 
which he had devoted his days, and which had filled his soul with 
the most elevated conceptions of nature and its divine Author. 
Subsequently to this, merely because he had the honesty to main- 
tain that the earth turned on its axis, he was condemned by a 
board of Cardinals to perpetual imprisonment. He did not long sur- 
vive the loss of his liberty. He died at the age of eighty-four years. 



SCIENTIFIC VIEW OF THE SOLAR SYSTEM. 

LESSON V. 

The Solar System consists of the Sun, the Planets, and the 
Comets. The term solar is derived from the Latin word Sol, 
which signifies Sun. Around the sun, the planets and the comets, 
in their respective orbits, constantly revolve. 

26. What fact is stated in proof of this ? 27. Who was Tycho Brahe ? 

28. When did he live ? 29. What was his system ? 30. Why did 

he form it ? 31. Who was Galileo ? 32. When did he live ? 

33. What enabled him to make more discoveries in the science than his pre- 
decessors ? 34. What was he compelled to do, when passed the age of 

seventy years ? 35. By whom ? 

1. Of what does the solar system consist i* 2. From what is the term 

solar derived ? 



12 FIRST BOOK IN ASTRONOMY. 

The sun is the centre of the solar system, and is the sotifce' q£ 
light and heat. Its form is nearly that of a sphere or globe. 

Planets are dense, dark bodies, resembling the globe, which w^ 
inhabit. Of course, they are not seen by their own light, but by 
the reflected light of the sun, which shines upon them. 

Planets are of two kinds. Primary and Secondary. The prima- 
ry planets are those which revolve immediately about the sun. 
The secondary are those which revolve about some of the primaries. 
Secondary planets are sometimes called moons or satellites. 

There are eleven primary planets; namely. Mercury, ^ ; 
Venus, 9; Earth, ©; Mars, i; Saturn, \i; Vesta, g; Juno, § ; 
Ceres, $; Pallas, $; Jupiter, 21 ', and Herschel, ^. Vesta, Juno, 
Ceres, and Pallas, are frequently called Minor Planets, and also 
Asteroids. 

Mercury and Venus are denominated Interior planets, because 
they are nearer the sun than the earth. All the others are called 
Exterior planets, because they are more distant from the sun than 
the earth ; or because their orbits are without the orbit of the earth. 

Five of the primary planets, at certain times are visible to the 
naked eye. They are Mercury, Venus, Mars, Jupiter, and Sat- 
urn. Herschel is too distant to be seen without the aid of a tel- 
escope, except rarely to a very good eye, in a clear night when the 
moon is absent, 

All the satellites of Jupiter, Saturn, and Herschel; and also the 
planets Ceres, Pallas, Juno, and Vesta, are invisible to the naked eye. 

The secondary planets are distributed among the primary planets 
in the following manner. Our earth has one, commonly called the 
the moon; Jupiter has four ; Saturn has seven ; and Herschel has six. 

All the planets, in their revolutions, move from west to east; 
unless there be an exception for the satellites of Herschel, which 
have been thought, by some astronomers, to revolve in a contrary 
direction. 

3. What is the centre of this system ? 4. What is the form of the sun ? 

, 5. What are planets ? 6. How are they seen ? 7. How many kinds 

of planets are there ?r 8. What are primary planets ? — — 9. What are secon- 
dary planets P-^ 10. By vjhat other name are secondary planets called : 

11. How many primary planets are there ? 12. What are their names ? 

13. Which ones are called asteroids ? 14. Which two are called interior 

planets? 15. Why.''-. 16. Which ones are called exterior planets.' 

1.7. Why are they so called.^ — ^—18. Which planets are seen by the naked 

eye ? 19. Is Herschel ever seen by the naked eye 1 20. When ? 

21. What ones are not seen by it?- 22. How are the secondary planets 

distributed among the primaries ? ^23. In what direction do the planets 

move? 24. Is there any exception,' 



FIRST BOOK IN ASTRONOMY. 13 

Mercury, Venus, Earth, Mars, and Saturn, are known to revolve 
round an imaginary line, passing through their centre, which is 
called their axis. The period of this revolution is called their day. 
The time, which a planet takes to revolve round the sun is called 
its year. 

The comets are wandering bodies, which revolve round the sun, 
in very eccentric orbits ; and are only seen when in that part of 
their orbit nearest the sun. 



DESCRIPTION OF AN ORRERY, OR PLANETARIUM, 
LESSON VI. 

An Offery, or planetarium, as it is sometimes called, is a ma- 
chine so constructed, as to represent, by the movement of its sev- 
eral parts, the motions and phases of the planets in their orbits. 

This machine was invented, in the seventeeth century, by George 
Graham, an eminent clock and watchmaker of London. Rowley, 
a workman, borrowed it of him, and made a copy for the Earl of 
Orrery, after whom it was named. 

Afl orrery may be considered as a diametrical section of the 
universe^ the upper and lower hemispheres being suppressed. 

On the upper plate, which answers to the ecliptic, are placed in 
two opposite but corresponding circles, the days of the month, and 
the signs of the ecliptic, with their respective characters. 

Through the centre of this plate is a stem, on which is a brass 
ball to represent the sun. Round this stem are different sockets to 
carry the arms by which the several planets are supported. 

The planets are represented by ivory balls, having the hemis- 
phere which is next the sun white, and the other black, to exhibit 
their respective phases. And these bails may be taken off, or put 
on, with ease, as occasion may require. 

About the primary planets are placed the secondary planets or 
moons; and by turning the handle, which communicates with a 

25. What planets are known to revolve on their axis ? 26. What period 

is a planet's day ? 27. What is its year ? 28. What are comets ? 

1, What is an orrery? 2. By what other name is it called? 3. By 

whom and when was it invented ? 4. Why was it called an orrery ? 

5. What part of the universe does it represent? 6. What is on the upper 

plate ? 7. By what is the sun represented ? 8. By what are the plan- 
ets represented ? 9. How are their hemispheres exhibited ? 10. What 

are placed about the primary planets ? 



14 FIRST BOOK IN ASTRONOMY. 

train of wheel work concealed in a circular box, the planets are put 
in motion, moving round the ball that represents the sun. 

If the ivory ball representing the earth, in an orrery, be taken 
as the standard, the other ivory balls will move with the same rela- 
tive velocities, and in the same periodical times, with which the 
planets traverse the regions of space. 

By placing a small lamp on the end of the central stem, instead 
of the brass ball representing the sun, and the most pleasing eflfects 
will be produced especially if the orrery be in a darkened room. 
The side of each ivory ball next to the lamp will be enlightened, 
while its opposite side will be shaded ; the same as the side of each 
planet next the sun is illuminated, while its opposite side is in 
darkness. 

If an orrery were put in motion by machinery, resembling an 
eight day clock, the revolutions of the planets would be represent- 
ed according to their exact times, as in nature. This is sometimes 
done in a large and expensive orrery. 



PERIODICAL REVOLUTION OF THE PLANETS. 
LESSON VII. 

There is nothing in nature more wonderful, or that more clearly 
shows the power and wisdom of God, than the revolution of the 
planets. They move in their orbits with so much precision and 
regularity, that no material variation takes place for ages, and even 
for thousands of years 

If a body be put in motion, by the application of a single force, 
it will move forward in a straight line. If several powers be dif- 
ferently applied to it, at the same time, as it cannot obey them all, 
it will obey no one of them, but will move in a direction between 
them. 

It is through the agency of this mechanical principle, that the 
heavenly bodies are enabled to perform their periodical revolutions. 

11. By what means are the planets put in motion? 12. What will be 

the consequence if the ivory ball, in the orrery, representing the earth, be 

taken as the standard ? 13. If a small lamp be put in the place of the brass 

ball representing the sun, what will be exhibited ? 14. How may an orrery 

be so constructed as to represent the exact times of the revolutions of the 
planets ? 15. Is this ever done ? 

1. What does the revolution of the planets show ? 2. How will a body 

move, if acted on by a single force ? 3. How will it move if acted on by 

several different forces at the same time ? 



FIRST BOOK IN ASTRONOMY. 15 

The application of two distinct forces, upon the planets in the solar 
system, acting in right angular direction, causes them to move in 
their orbits. One of these forces is called centrifugal, and the 
other centripetal. 

The centrifugal force, which is also called the projectile power, 
impels the planet forward in a straight line. The centripetal force, 
which is the same thing as gravitation, draws the planet to a fixed 
point. These two forces act upon each so equally, as to cause the 
planet to move round a given point called the centre of gravity. 

In Plate IV, Fig. 3, let S represent the sun, A the earth, and 
A D G I the earth's orbit. If the earth A were operated on by the 
centrifugal force only, it would be carried forward to the letter B. 
If it were operated on by the centripetal force only, it would be 
drawn directly to the sun S. But the earth A being acted on by 
these two forces united, it is carried to the letter D; and, then 
in like manner to the letter G, and finally again to the letter A 
where it originally started. 

A simple illustration of circular motion, can easily be made, by 
a stone fastened to the end of a string. Let the other end of the 
string be held in the hand, and the stone, whirled round. The 
stone being confined to the hand, by the string, will move 
roupd it, in a circular form, as the earth or any other planet moves 
round the sun. In this experiment the string represents gravita- 
tion, or the centripetal force ; and the power which puts the stone 
in motion represents the centrifugal force. 

Mercury performs its revolution about the sun in 88 days ; Venus, 
in 244,2-3; the Earth, in 366 1-4 ; Mars, in 687 ; Vesta, in 
1335,1-4; Juno, in 1591; Ceres, in 1681,1-2; Pallas, in 
1681, 2-3 ; Jupiter, in 4332, 3-5 ; Saturn, in 10759 ; and Her- 
schel, in 30682, 2-3 days. 

It will be seen from the above table, that the length of the years, 
in the different planets, is regularly in proportion to the distance 



4. What are the two forces called in the production of circular motion ? 

5. By what other name is centrifugal force called ? 6. What power is 

the same as the centripetal force 7. How is circular motion illustrated 

by Fig. 3, of Plate IV ? 8. How may circular motion be represented by 

the whirling of a stone ? 9. In this experiment what represents the cen- 
trifugal force ? 10. What the centripetal ? 11. How many of our years 

are equal to one year of Herschel ? 12. To one year of Saturn ? 13. To 

one year of Jupiter ? 14. To one year of Mars ? 15. How many years 

of Mercury are equal to one of Herschel ? 16. How many years of Mars 

are equal to one of Saturn ? 17. How many of Venus to one of Jupiter.^ 

18. In what proportion do the years of the different planets vary in length ? 



k 



16 FIRST BOOK IN ASTRONOMY. 

they are from the sun. The four minor planets, or asteroids, which 
are about equally distant from the sun, perform their revolutions in 
nearly the same period. 

Motion, in astronomy, may be divided into real and apparent. 
Real motion is the actual movement of any body ; as the revolution 
of the earth. Apparent motion is when a body appears to move, 
but is actually at rest ; as the apparent motion of the sun and stars, 
produced by the real motion of the earth. 



DIFFERENT THEORIES OF THE SUN. 
LESSON VIII. 

The sun has ever been esteemed an object of the first importance 
in the solar system. Being the great source of light and heat, 
it diffuses its rays to every part of an immense sphere, giving life 
and motion to innumerable objects. Like its divine Author, while 
it controls the greatest, it does not overlook the most minute por- 
tions of the creation. 

According to the Copernican system, now universally received, 
the sun is the centre of all the planetary and cometary motions, all 
the planets and comets revolving round it in different periods, 
and at different distances'. The sun, although stationary in respect 
to surrounding objects, is not destitute of motion. It turns on its 
own axis, from west to east, in about twenty-five days. 

There has been much speculation concerning the physical or- 
ganization of the sun. It was formerly supposed to consist of liq- 
uid fire, exhaustless in its nature ; which, by constantly emitting 
rays in every direction, imparted a cheering influence to every part 
of the system. By modern astronomers this theory has been found 
untrue. They have supposed, with more plausibility, that it is a 
solid body, surrounded by a luminous atmosphere. 

It is estimated that the atmosphere with which the sun is sur- 
rounded, extends to the distance of two thousand miles from its 
surface ; and, that its density is at least eighty times greater than 
that which environs the earth. Herschel supposes that the density 

19. Which four planets have years about of the same length ? 20. What 

is the difference between real and apparent motion in astronomy ? 

1. Why has the sun always been an interesting object? 2. What mo- 
tion has it ? 3. Of what was it formerly supposed to consist?— 4. How 

do modern astronomers jview the sun, as to its physical organization ? 

5. What is said of the density of the sun's atmosphere? 6. And of its 

height ? 



FIRST BOOK IN ASTRONOMY. 17 

of the luminous solar clouds need not be greater than that of our 
Aurora Borealis, to produce the effects with which we are ac- 
quainted. Euler makes the light of the sun equal to 6500 candles 
at a foot distance. 

A knowledge of chemical agencies, as made known in modern 
scientific discoveries, makes it highly probable that the heat and 
light of the sun are occasioned by some invisible action between 
the atmosphere of the sun and the atmosphere of other bodies. 
The collision of a flint against steel, not only causes heat, but pro- 
duces fire ; and the action of water upon lime, not only causes heat, 
but forces the water to fly off in steam. 

The sun is a spherical body, and has a diameter of about 880,000 
miles; being more than equal to 100 diameters of the earth. So 
great is the power of gravitation upon its surface, that a body 
weighing one pound at the surface of the earth, will there weigh 
about thirty pounds. Thus a common sized man removed to the 
surface of the sun would weigh between two and three tons. 

On different parts of the sun's disc may be seen dark spots, cg,lled 
maculm. These consist of a nucleus, which is much darker than 
the rest, surrounded by a mist or smoke; and they are so change- 
able as frequently to vary during the time of observation. Some of 
the largest of them seem to exceed the bulk of the whole earth, and 
are often seen for three months together. They were first observed 
by the celebrated Galileo. 

Some have supposed these spots to be deep cavities in the body 
of the sun ; some have supposed them to be the smoke of volcanoes, 
or the scum floating upon a huge ocean of fluid matter ; and others, 
among whom was Dr. Herschel^ supposed that the spots are nothing 
else than portions of the opaque body of the sun, perhaps high 
mountains, seen in consequence of the accidental opening of the 
luminous atmosphere wqth which the sun is overshadowed. 

The similarity of the sun to the other globes of the system, in 
solidity, atmosphere, surface diversified with mountains and vallies, 



7. What comparison does Herschel make between its atmosphere, and the 

Aurora Borealis ? 8. How did Euler estimate its light? 9. How is it 

supposed that the light and heat of the sun may be produced ? 10. In sup- 
port of this supposition what two illustrations are given ? 11. What is the 

form of the sun ? 12. What is its diameter.^ 13. How does it compare 

with the diameter of the earth ? 14. What comparison is made between 

the gravitation of the sun and of the earth .'' 15. How much would a com- 
mon sized man weigh removed to the surface of the sun ? 16. How large 

are some of the spots on the sun's disc.^ 17. By whom were they first 

observed ^ 18. What have these spots been supposed to be ? 



IS FIRST BOOK IN ASTRONONY. 

and rotation on its axis, lead us to conjecture that it is inhabited, 
like the rest of the planets, by beings whose organs are adapted to 
their peculiar circumstances. 

Dr. Elliot, an English astronomer, allows his imagination, in 
speaking of it, to depict the most delightful rural scenery, with purling 
brooks, meandering streams, and rolling oceans, and with all the 
vicissitudes of foul and fair weather. And as the light of the suri i» 
eternal, so he imagined, were its seasons. Hence, the Doctor infers, 
that this luminary offers one of the most blissful habitations which 
the mind of man is capable of conceiving. 



MAGNITUDES AND PLACES OF THE PLANETS. 
LESSON IX. 

A person unacquainted with the effect produced on the appa- 
rent magnitude of a body, by change of distance, would be likely 
to conclude that the moon is larger than either of the other planets 
in the system. But this is found to be an optical illusion. The 
diameter of the moon is only about half equal to the diameter of 
Mercury, the smallest of the seven principal primary planets. 

Although the planets, viewed by the naked eye, seem to occupy 
but a mere point of space, yet this is owing to the great distance 
at which they are placed from us. The earth viewed from one of 
the remote planets would appear as they now appear to us ; and 
our sun, seen from a still further distant part of the heavens, would 
appear like one of the fixed stars. 

A child can easily make observations in illustration of such 
effects. A man, at the distance of half a mile from us, will appear 
in size like a boy of fifteen years ; and other objects, by being re- 
moved from us, will lose a corresponding portion of their apparent 



19. What inference may we draw from the analogy between the form and 

organization of the sun and of the planets? 20. What was Dr. Elliot's 

opinion on the subject ? 

1. Who would be likely to consider the moon the largest planet in the sys- 
tem ? 2. How does the diameter of the moon compare with that of Mercu- 
ry ? 3. Why do the planefs appear so small ? 4. How would the earth 

appear viewed at one of the distant planets? 5. How would the sun 

appear viewed at a more distant part of the universe? 6. What is said of 

tlie apparent size of a man, seen at a distance ? 



IRJBILAMMB SUZJES m TMM iPI^AESBTS 



£Cjzr 




FIRST BOOK IN ASTRONOJMY. 19 

magnitude. A large kite, as it rises in the air, is gradually dimin- 
ishing in apparent size till it dwindles into a mere black speck, and 
at last is entirely lost to the sight. So also it is with birds as they 
soar in the regions above us. 

To avoid the labor of committing to memory in miles, the sever- 
al distances, at which the planets are situated from the sun, astron- 
omers have adopted a more simple method. The distance between 
Herschel and the sun is supposed to be divided into one hundred 
and ninety-five parts. Mercury is estimated at four of these parts 
from the sun ; Venus, at seven; the Earth, at i^eTz; Mars, ^i fifteen; 
Jn^hex^dX fifty -two; Saturn, dii ninety five ; and Herschel, as al- 
ready given, at one hundred and ninety-five. 

These proportionate distances rnay not be perfectly accurate ; but 
they are sufficiently so to answer all needed purposes in a work like 
the present. They are obtained by multiplying the respective dis- 
tances of the planets by ten, and dividing the product by ninety-five, 
tlie mean distance of the earth from the sun. 

A similar plan has been proposed for fixing with facility in the 
mind the comparative magnitudes of the planets. Thus the Earth 
is computed to he fourteen times as large as Mercury ; a very little 
larger than Venus,- three times as large as Mars; and more than a 
million times as large as Pallas. But Jupiter is more ih^^w fourteen 
hiindred times as large as the earth ; Saturn, exclusive of his ring, 
above a thous and iimes^s large; and Herschel eighty times as large. 

The bulk of the sun is one million and four hundred thousand 
times the bulk of the earth; but as its density is less than one fourth 
of that of the earth, it has only about 333 thousand times as much 
matter. It may, therefore, be concluded that the sun contains, at 
least, three hundred thousand times as much matter as all the planets 
in the solar system. 

The following is another method of fixing on the mind an idea of 
the relative size of the sun and planets. Supposing a globe of 24 
inches diameter to be the size of the sun, the proportionate diam- 
eter of Mercury would be about one eighth of an inch — of Venus, 

7. What is said of a kite as it rises in the air? 8. Has any more simple 

method of remembering the relative distances of the planets been adopted 

than committing to memory their real distance ? 9. If the distance of 

Herschel from the sun be divided into 195 parts, how many of these parts 

will Mercury be ? 10. How many Venus ? 11. Hov/ many the Earth ? 

1'2. How many Mars ? 13. How many Jupiter .' 14. How many 

Saturn.'' 15. How are the j)roportionate distances found.' 16. How 

does the Eartli compare with Mercury in size .' 17. With Venus.? . 

18. With Mars.? 19. With Pallas .? 20. With Jupiter .' 21. With 

Saturn .? 22. With Herschbl .? 23. With the Sun .? 24. If a 24 inch 

globe represent the size of the Sun, what would be the proportionate diame-^ 
ter of Mercury ? 



20 FIRST BOOK IN ASTRONOMY. 

one fifth of an inch — of the Earth, one fourth of an inch — of 
Mars, one sixth of an inch — of Jupiter, two inches and one half — of 
Saturn, one inch and nine tenths — and of Herschel, one inch and 
one tenth. 

According to these proportions of their bulk, Mercury would be 
about 32 yards from the centre of the sun ; Venus, 60 yards ; the 
Earth, 82 yards; Mars, 126 yards; Jupiter, 340 yards ; Saturn, 
788 yards; and Herschel, 1570 yards. In this proportion, the 
moon's distance from the centre of the earth, would be only seven 
inches and a half 

Again ; suppose, that a body projected from the sun should con- 
tinue to fly with the swiftness of a cannon ball, which is at the rate 
of 480 miles an hour; this body would reach the orbit of Mercury 
in 8 years 290 days; of Venus, in 16 years 59 days ; of the Earth, 
in 22 years 211 days; of Mars, in 34 years 82 days ; of Jupiter, in 
116 years and 116 days; of Saturn, 213 years ?29days; and of 
Herschel, in 427 years 290 days. 



AN ACCOUNT OF MERCURY AND VENUS 
LESSON X. 

Mercury is the planet nearest the sun, and its orbit is consequent- 
ly contained within the orbit of the earth. It is also the most 
dense of all the planets belonging to the solar system : and as its 
situation is next to the sun, so the portion of solar light and heat 
imparted to it, is much greater than that received by any of the 
other planets. 

Mercury may be seen when crossing the sun's disc, which some- 
times happens; and also when west of the sun, just before sunrise, 
and Vi^hen east of the sun, a little after sunset. The light of this 
planet is very white and dazzling, and appears to twinkle like the 
light of a fixed star. 

25. Of the Earth? 26. Of Jupiter? 27. Of Saturn? 28. Of Her- 

schel? 29. And with these proportions of their bulk, what would be the 

distance of the earth from the centre of the sun ? 30. And of the moon 

from the centre of the earth ? 31. At what rate does a cannon ball move ? 

32. At this rate, how long would it take a body to come from the sun to 

the orbit of the earth ? 33. And to the orbit of Herschel? 

1. Which planet is nearest the sun ? 2. What is said of the density of 

Mercury ? 3. When may it be seen ? 4. What is said of its 

light ? 



FIRST BOOK IN ASTRONOMY. 21 

When viewed with a telescope of high magnifying power, Mer- 
cury exhibits nearly the same phases as the moon, and they are to 
be accounted for in the same manner. But, owing to the splen- 
dor of its light, and the intense brightness of the sun, astronomers 
have been unable to make any very extensive or accurate discov- 
eries in this planet. 

Mr. Shroeter imagined that he discovered not only spots on the 
disc of Mercury, but even high mountains. He affirmed that one 
was more than ten miles in height ; nearly three times as high as 
Chimborazo in South America. Dr. Herschel was unable to dis- 
cover any thing of the kind. 

The intensity of the sun's light and heat at Mercury is about 
seven times greater than at the earth, in the middle of our summer ; 
which, as Sir Isaac Newton found by experiments made for that 
purpose, w^ith a thermometer, is sufScient to make water fly off in 
steam. Such a degree of heat must render this planet uninhabita- 
ble to creatures of our constitution ; but we may presume that the 
inhabitants of this planet are formed with natures suited to their 
situation ; so that they may have as many comforts and enjoyments 
in point of residence as we have. 

Mercury revolves round the sun, at nearly the distance of thirty 
millions of miles, and completes its revolution in about three months. 
The velocity of Mercury in revolving about its axis is about twenty- 
eight miles an hour; and in its orbit about the sun, more than 
100,000 miles an hour. So great is the rapidity with which it 
moves, that the Grecian astronomers considered it the messenger 
of the gods ; and hence they represented it with wings at its head 
and feet, from which is derived ( ^ ) the character used to repre- 
sent it. 

It would require 20,000,000 bodies of the magnitude of this 
planet to make one of equal size to the sun. 

Venus revolves in an orbit between the orbit of the earth, and that 
of Mercury, being a distance of sixty-eight millions of miles from 



5. Of its phases ? G. Why have not more astronomical discoveries been 

made respecting it ? 7. What discovery did Mr. Shroeter affirm he had 

made ? 8. How do the light and heat of this planet, compare with what 

is experienced at the earth ? 9. What experiment did Sir Isaac Newton 

make on the heat of Mercury ? 10. What is said of its being inhabited ? 

11. How far distant fromthe sun isMeicury .'' 12. In what time does 

it revolve about it ? 13. What is the velocity of Mercury in its orbit.' 

14. And on its axis .' 15. How did the Grecian astronomers view this 

planet ? 16. How does it compare in magnitude with the sun .' 17. Where 

is Venus situated ? 



22 FIRST BOOK IN ASTRONOMY. 

the sun. This revolution is completed in about seven an a half of 
our months, turning on its axis in a little less than twenty-four hours. 
Venus moves in its orbit, at the rate of 75,000 miles an hour. 

Venus is the most beautiful, and, as presented to the naked eye, 
the largest of the primary planets. Its light is white and very 
brilliant. Once in about eight years, when brightest, it is calcu- 
lated that Venus may be seen at noonday. When at the vpestof the 
sun, it rises before the sun, and is called the morning star ; when, 
appearing at the east of the sun, it shines in the evening, and is 
called the evening star. It is in each situation alternately for about 
two hundred and ninety days. 

Although the moon reflects more light than Venus does, yet this 
light is dull, and has none of the briskness which attends the beams 
of Venus. This difference is supposed to arise from the circum- 
stance of Venus having an atmosphere far more dense than that of 
the moon. This atmosphere has been estimated to be fifty miles 
in height. The solar light and heat at the surface of Venus are 
about double of what is experienced at the earth. 

Venus exhibits all the moon-like phases which Mercury does ; 
and, like Mercury, is sometimes seen passing over the sun's disc, in 
the form of a dark round spot. This is called the transit of Venus, 
and is a rare occurrence, and one which has very much excited the 
attention of astronomers. During the last century there were two 
transits ; one in June, 1761, and the other in 1769. No other one 
will occur till the year 1874. 

There have been discovered on this planet dark spots ; and, on 
its borders, irregular, but brilliant shades. These telescopic ap- 
pearances may be examined in figures 1, 2, 3, 4,5, and 6, of Plate 
IV. High mountains have also been discovered in Venus, partic- 
ularly one in the southern hemisphere, which is estimated to be 
twenty-two miles high ; about four times the height of the most 
elevated mountains on our globe. 



18. In what time does it perform a revolution in its orbit ? 19. And on 

its axis .'' 20. What is the velocity of Venus in its orbit .'' 21. What is 

said of the appearance of Venus.'' 22. What takes place with it once in 

eight years .'' 23. When is Venus the evening star.'' 24. When the 

morning star .? 2-5. How long time does it continue in each situation ? 

2G. How does the light of Venus compare with that of the moon 7 27. Why 

is it more beautiful .' 28. How high is the atmosphere of Venus ? 

29. How do the solar light and heat at Venus compare with what is experi- 
enced at the earth.'' 30. What is said of the phases of Venus.'' 31. What 

is meant by the transit of Venus.' 32. When has this taken place.? 

33. When will it again? 34. What telescopic discoveries have been made 

on Venus .' 35. By which figures are these appearances exhibited .' 

36. What is said of a mountain discovered there ? 



FIRST BOOK IN ASTRONOMY. 23 

ASTRONOMICAL VIEW OF THE EARTH. 

LESSON XI. 

The earth is round or spherical, like all the other planets. 
This is proved, by its shadow on the moon, in lunar eclipses; 
by its own convexity, as exhibited in the appearance of a vessel 
at sea ; and by the fact, that it has frequently been sailed round 
or circumnavigated. The hills and valleys, on its surface, de- 
tracting no more from its rotundity, than the proturberances in the 
rind of an orang<^ prevent that fruit from being circular. 

The earth is situated next to Venus, in distance from the sun. 
Its mean distance from that luminary is about 95 millions of 
miles. The revolution of the earth about the sun is performed 
in a little more than 365 days.* This period is called a year. 
It moves in its orbit, at the rate of 6S,G00 miles an hour, which 
is about 1100 miles a minute. 

That such a velocity should be imperceptible, may shock the 
credulity of those who are unaccustomed to the contemplation of 
such objects. But we are to consider, that every object around, 
even the atmosphere, is carried with us ; so that there is nothing 
by which we can compare our motion, except the heavenly bodies. 
By observations on these, such motion is now rendered past doubt. 

The velocity of the earth's motion being imperceptible, is not 
wonderful to those who have sailed in a ship or boat on still water. 
There, a person, having obtained the motion of the vessel, feels no 
inconvenience from its swiftness, and is nearly insensible of move- 
ment, except from surrounding objects, till he strikes a shore or 
other obstruction. The motion of the earth is far more uniform and 
even, than any movement on the stillest water. 

Besides the motion of the earth round the sun, it revolves on its 
own axis, once in twenty-four hours. The regular succession of 
day and night is occasioned by this revolution on its axis ; the sun 
and all the heavenly bodies appearing to rise in the east, above the 



365 days, 5 hours. 48 minuteS; and 51.G seconds. 



1. How is it shown that the earth is globular? 2. What is said of its 

hills and valleys? 3. What is the distance of the earth from the sun ? 

4. What is the time of its revolution ? 5. What is its velocity in its orbit ;*• 

6. What objection might be made to the idea of so much velocity in the 

earth's motion ? 7. How is this reconciled to our experience ? S. What 

comparison is made between the motion of the earth, and of a vessel on the 

water? 9. How often does the earth revolve on its axis? 10. WhaV 

sensible effects result from the motion of the earth on its axis ? 



24 FIRST BOOK IN ASTRONOMY. 

horizon ; to ascend to their meridian height ; and, then, in the 
west, to sink below the horizon. 

The path or tract in wliich the sun appears to move round the 
earth is called the ecliptic. It is called by this name, because all 
the eclipses of the sun and moon happen when the moon croses this 
path, or is nearly in one of tiiose parts of her orbit where it crosses 
this path. The points in which the moon's orbit crosses the 
ecliptic are called the moon's nodes. 

The earth viewed, at the moon, will exhibit much the same 
changes, as seen by us, in that body. But the earth appears more 
than thirteen times larger when viewed from the moon, than the 
moon appears to us ; and hence, far more luminous. When the 
moon is new to us, the earth will appear full to that satellite, and 
the contrary. 



DESCRIPTION OF ARTIFICIAL GLOBES. 

LESSON XII. 

There are two kinds of artificial globes, terrestrial and celestial. 
On the terrestrial is represented the surface of the earth, diversi- 
fied with land, water, and the principal divisions of each, forming a 
spherical map of the whole. On the celestial is represented the 
visible heavens, as distinguished into constellations, by the picture 
of the animal or other object of the constellation, and the principal 
stars by which it is formed. 

The globes commonly used are composed of plaster on which 
the maps, or descriptions, are pasted. When finished, they are 
hung in a brass meridian, with an hour circle, and a quadrant, and 
fitted into a wooden horizon. There are two kinds of circles 
drawn on artificial globes ; the greater and the lesser. The^rea^- 
er circles divide the globe into equal parts; these are the equator, 
the ecliptic, the meridian, and the horizon. The lesser circles di- 
vide it into unequal parts ; these are tropics, the polar circles, and 
the parallels of latitude. 



II. What is the ecliptic ? 12. Why is it so called .' 13. What are the 

moon's nodes .' 14. How would the earth appear viewed at the moon ? 

15. With whn.t difference in apparent size .' 16. With what variation 

as to time ? 

1. How many kinds of artificial globes are there.'' 2. What is repre- 
sented on the terrestrial .'' 3. What on the celestial .-' 4. How are globes 

made .' 5. What are greater circles .-* 6. What, are lesser circles .'' 



FIRST £00K IN ASTRONOMY. 2S 

The axis of the earth is an imaginary line passing through the 
centre of it, from north to south, upon which is produced its diurnal 
motion, causing its regular succession of day and night. The axis 
is represented by the wire on which the globe turns. The poles of 
the earth are the extremities of its axis. One is called the north, 
and the other the south pole. 

The equator is an imaginary line extending around the centre ot 
the globe, from east to west, equally distant from the poles, and di- 
viding it into northern and southern hemispheres. The equator on 
the celestial globe is called the equinoctial. The ecliptic is repre- 
sented on the globe by a circle cutting the equator with an angle 
of 23^ degrees. 

Latitude, on the terrestrial globe, is the distance of any place 
from the equator, either north or south. It is reckoned in degrees 
and minutes, or in geographical miles, on the brass meridian, 
from the equator to the poles. The highest latitude of any place 
cannot exceed 90 degrees. 

The tro])ic of Cancer is a circle 232 degrees north of the equa- 
tor and parallel to it. The tropic of Capricorn is a circle 23^ de- 
grees south of the equator and parallel to it. The arctic circle is 
a line 662 degrees north of the equator and parallel to it; beino- 
also 23^ degrees from the north pole. The antarctic circle is a 
line QQi degrees, south of the equator and parallel to it ; being al- 
so 23^ degrees from the south pole. 

The brass ring, in which an artificial globe is sus{>ended, is call* 
ed the hrass meridian. It is divided into 360 degrees, each 
quadrant or quarter containing 90 degrees. This circle divides 
the globe into two equal parts called eastern and western hem- 
ispheres. 

Meridian lines are those circles drawn on a globe through the 
poles, and cutting the equator at right angles. There are usually 
24, and consequently 15 degrees distant from each other. They 
denote the longitude of the places over which they pass. The de* 



7. What is the axis of the earth ? 8- How is it represented on the globe .? 

0. What are the poles ? 10. How are they distinguished from each 

other ? 11. What is the equator ? 12. What is it called on the celestial 

globe ? 13. How is the ecliptic drawn ? 14. What is latitude ? 

1-5. How is it reckoned ? 16. What is the highest latitude .' —17. What 

is the tropic of Cancer ? 18. What is the tropic of Capricorn .'' 19. What 

is the arctic circle .' 20. What is the antarctic circle ? -21. What is said 

of the brass meridian .'' 22. What are meridian lines .' 23. How many 

are there ^ 24. How far distant are they from each other .'' 25. What 

do they denote ? 

D 



2d' FIRST BOOK IN ASTRONOMY. 

grees of longitude eastward and westward are marked on the 
equator. Longitude is usually reckoned from Greenwich near 
London. 

Latitude on the celestial globe, is the distance of any star or 
planet, from the ecliptic, either north or south of that circle. 
Longitude, on this globe, means the distance of any planet or star 
from the first degree of Aries. 

The quadrant of altitude is a thin slip of brass, divided into de- 
grees. It is so contrived as to be capable of being fixed to any part 
of the brazen meridian. 

The zenith is a point in the heavens directly over head. On the 
artificial globes, it is the elevated pole of the horizon, and ninety 
degrees above it. The nadir is a point directly under foot, and is 
the depressed pole of the horizon. 

The horizon is an imaginary great circle in the heavens, which 
divides the celestial sphere into two equal parts, called upper and 
lower hemispheres. We usually call the circle which bounds our 
prospect, or where the sky and the earth appear to meet, the hori- 
zon. But this, by way of distinction, is denominated the sensible 
horizon. The rational horizon is the great circle, which divides 
the earth into two equal parts, being parallel to the plain of the sen- 
sible horizon. The rational horizon is represented by the broad 
thin wood circle in which the globe is suspended. 

The colures are two great circles, supposed to intersect each 
other at right angles in the poles of the earth, and to pass through 
what are called the solstitial and equinoctial points of the ecliptic. 
The equinoctial points are Aries and Libra : the solstitial points 
are Cancer and Capricorn. These divisions of the ecliptic mark 
the seasons of the year. 

The zodiac, on the celestial globe, extends eight degrees each 
side of the ecliptic ; making a girdle or belt in the heavens, six- 
teen degrees in width. Within this space revolve all the planets, 
with the exception of Ceres, Pallas, and Juno. A more particular 
account will be given of the zodiac in the lesson on the con- 
stellations. 

26. From what place is longitude usually reckoned ? 27. What is lati- 
tude on the celestial globe ? 28. What is longitude on the celestial globe ? 

29. What is the quadrant of altitude ? 30. What is the zenith ? 

31. What is the nadir? 32. What is the horizon? 33. What is the 

sensible horizon? 34. What is the rational horizon? 35. By what is it 

represented ? 36. What are the colures ? 37. What are the equinoc- 
tial points .? 38. What are the solstitial points r 39. What is the use 

of these points ? 40. What is the zodiac ? 



flatj: nr 




O.TeltOTv So. 



FIRST BOOK IN ASTRONOMY. 27 

The hour circles of an artificial globe are drawn around the poles 
in the form of a clock dial. They are divided into 24 equal parts, 
corresponding to the hours of the day. To these circles, an index 
or pointer is fixed, for the purpose of pointing out the hour. 



ELEMENTARY ACCOUNT OF MARS. 
LESSON XIII. 

Mars, the planet next to the earth, in distance from the sun, is 
distinguished by the remarkable dusky red color of its light; by 
the great number and the diversified appearance of spots seen upon 
its surface ; and by the brightness of its polar regions. 

The dusky red appearance of Mars is thought to be owing to a 
thick atmosphere with which it is surrounded ; and the brightness 
about the poles is supposed to be occasioned by large quantities of 
snow and ice which there exist. 

From the red appearance of this planet, it was by the ancients 
called Mars, wJiich is the same as God of War ; and it is repre- 
sented by a character {$) denoting a man with a spear in his 
hand. The same character is also used to represent iron among 
metals. 

The whole disc of Mars generally appears illuminated ; though 
at times, permanent dark spots have eclipsed its brilliancy ; and 
sometimes it has a gibbous appearance, that is, its disc is more than 
half, but not wholly illuminated. 

Dr. Herschel noticed occasional changes of partial bright belts 
near the equatorial regions of this planet; and on one occasion, he 
noticed a darkish one in a high latitude. These he ascribes to 
the clouds and vapors, which float in the atmosphere of Mars. 
Some of the most remarkable telescopic appearances of this planet 
may be seen in figures 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, and 
18, of Plate IV. 



41. What are the hour circles ? 

1. By what is Mars distinguished ? 2. To what is its red dusky appear- 
ance owing ? 3. To what is the brightness about the poles owing ? 

4. From what did this planet derive its name ? 5. What character repre- 
sents it? G. What else does this character denote ? 7. How does the 

disc of Mars appear ? 3. What did Herschel observe on it ? 9. To what 

did he ascribe them ? 10. Which figures represent them ? 



38 FIRST BOOK IN ASTRONOMY. 

Mars revolves round the sun in the period of 687 days, or a little 
less than two of our years. Its mean distance from the sun is 
144,000,000 of miles; moving in its orbit at thd rate of 55,000 
miles an hour. 

This planet sometimes rises before the sun, and becomes a 
morning star. Sometimes it sets after the sun, and then becomes 
an evening star. It is also seen, at other times, in the same part 
of the heavens with the sun, and beyond that luminary, being in 
conjunction. 

The inhabitants of Mars have three interior planets. Mercury, 
Venus, and the Earth. Each of these vAW sometimes be a morning 
star, and sometimes an evening star ; although the earth will be 
the brightest and most luminous. 

Summer and winter at Mars, are each about twice as long as 
they are on the earth ; and the proportion of light and heat receiv- 
ed from the sun is less than one half of what is enjoyed at the earth. 



VESTA, JUNO^ PALLAS, AND CERES. 
LESSON XIV. 

These four planets revolve in orbits between those of Mars and 
Jupiter. They have been recently discovered, and are so very 
small compared with the other primary planets, that they are fre- 
quently called asteroids ; or bodies having the appearance of stars. 

Ceres was discovered in the year 1801 ; Pallas, in 1802; Juno, 
in 1804; and Vesta, in 1807. Ceres was discovered by Piazzi, an 
Italian ; Juno, by Mr. Harding, a German ; and Pallas and Vesta, 
by Dr. Olbers, of Bremen. 

It has been supposed that these bodies are the largest fragments 
of a great planet, which once revolved in an orbit about midway 
between Mars and Jupiter ; and which, either by some internal 
convulsion, or external violence, has been separated into these, and 
probably many other smaller parts. 

11. In what time does Mars revolve in its orbit? 12. What is its ve- 
locity ? 13. How far is it I'roin the sun ? 14. When is Mars a morning 

star ? 15, When an evening star ? 16. When, else is it seen ? 

J7. How niany interior planets has it ? 18. What are they? 19. Which 

is the brightest.'' 20. What is said of the seasons of Mars.'' 21. And of 

its light and heat ? 

1. By what name are Vesta, Juno, Pallas, and Ceres called .? 2. Why- 
are they called asteroids.? 3. When and by whom was each of them dis- 

povered i* 4. What hq,s been supposed as to the origin of these planets.? 



FIRST BOOK IN ASTRONOMY. 29 

Against the above supposition, it is urged, that if the asteroids 
formerly constituted one large planet, it wouid have been seen by 
ancient astronomers, and enumerated among the planets. It is 
also supposed that the idea of an explosive force, that would over- 
come the mutual attraction of the parts separated, and cause them 
to fly forty millions of miles asunder, is most extravagant. 

The mean distances of these planets from the sun has been cal- 
culated as follows : Vesta, 225,000,000 of miles; Juno, 252,000,000 
of miles ; Ceres, 263,000,000 of miles ; and Pallas, 265,000,000 
of miles. The light and heat received by them from the sun, is 
about one ninth as great as at the earth. 

Vesta performs its revolution about the sun, in three years and 
two months; Juno, in four years, four months, and eight days; 
Ceres, in four years, seven months, and ten days ; and Pallas, in 
four years, seven months, and eleven days. By this it will be seen 
that Ceres and Pallas differ but one day in the time of their rev- 
olution. 

These newly discovered planets exhibit various changes in ap- 
pearance and size; so that their real magnitude has not been as- 
certained with certainty. The diameter of the largest has been 
computed at 2000 miles, and the smallest at 80 miles. Their 
density is somewhat more than twice the density of water. 

Ceres is surrounded with a dense atmosphere, which is estimat- 
ed, by Shroeter, the German astronomer, to extend to the height 
of 676 miles. The atmosphere of Pallas is 46S miles in height. 



ELEMENTARY ACCOUNT OF JUPITER. 

LESSON XV. 

Jupiter is much the largest planet in the solar system. The 
diameter of it is eighty-nine thousand miles. It is distant from the 
sun 490 millions of miles, revolving round it in a little less than 

5. What two objections are made to the idea that these planets are frag- 
ments of one large planet ? 6. What is the mean distance of Vesta from 

the sun ? 7. Of Juno ? 8. Of Ceres ? 9. Of Pallas ? 10. What 

degree of light and heat do they enjoy? 11. In what time does Vesta 

perform its revolution ? 12. In what time does Juno ? 13. In what 

tIme*does Ceres ? 14. In what time does Pallas ? 15. How much do 

Ceres and Pallas differ in the time of their revolution ? 16. What is said 

of the changes of these planets ? 17. Of their size ? 18. Of the atmos- 
phere of Ceres ? 19. Of the atmosphere of Pallas ? 

X. What is the relative size of Jupiter ? -2. What is its diameter .' 



30 FIRST BOOK IN ASTRONONY. 

twelve of our years. It turns on its axis in less than ten 
hours. • 

Jupiter has nearly fourteen hundred times the bulk of the earth; 
but its density being only 1^ to water, it contains about 300 as 
much matter as the earth. The amount of light enjoyed at Jupiter, 
is about one twenty-fifth part of what is enjoyed at the earth. 

The great bulk of this planet, and the short space of time in 
which it revolves on its axis, cause the velocity of its equatorial 
parts to be prodigiously great ; being not less than 26,000 miles 
per hour. 

Although Jupiter is about sixteen times farther from us than we 
are from Venus; and although the solar light on this planet is only 
about one fiftieth part of what is had at Venus ; yet to the naked 
eye, Jupiter frequently appears as large as Venus. 

On account of its superiority in size among the planets, this one 
is called Jupiter; that being the name of the most distinguished of 
the heathen deities. It is represented by this character, (^) to 
denote its whiteness, the same being used to denote tin among 
other metals. 

As the axis of this planet has no inclination, there is no change 
of seasons: in the polar regions there being perpetual winter, and 
about the equator perpetual summer. Were the axis inclined like 
that of the earth, one portion of its surface would alternately be de- 
prived of the sun's light, and have constant day for nearly the 
space of six of our years. 

Jupiter appears to be surrounded with belts, which are supposed 
to be clouds floating in the atmosphere. These belts are always 
parallel to his equator, and are interspersed with dark spots, which 
are supposed to be clouds more dense than the others. By observ- 
ing these spots through a telescope, the time of Jupiter's rotation 
on its axis has been ascertained. These belts and spots are repre- 
sented in figures 19, 20, and 21, of Plate IV. 

3. How far from the sun is it ? 4. In what time does it revolve round 

the sun ? 5. In what time does it turn on its axis ?■ 6. How does Jupiter 

compare with the earth in bulk and quantity of matter ? 7. What is its 

density ? 8. What is the velocity of its diurnal motion ? 9. How much 

farther from us is Jupiter than Venus ? 10. What is the proportionate 

degree with which Jupiter and Venus are seen by us ? 11. What is their 

comparative appearance, seen by the naked eye ? 12. Why is this planet 

called Jupiter .'' 13. By what character is it represented .' 14. What is 

said of its summer and winter ? 15. Why is this ? 16. What would be 

the consequence if the axis of Jupiter were inclined like that of the earth ? 

17. With what is Jupiter surrounded .' 18. Jn what direction do 

these belts extend ? 19. What are they supposed to be ? 20. Which 

figures represent them ? 



FIRST BOOK IN ASTRONOMY. 81 

As if to compensate, in part, for the want of light occasioned by 
ts remoteness from the sun, Jupiter is constantly attended by four 
moons or satellites, which revolve round it. These moons are too 
distant from us to be seen by the naked eye ; but with a telescope 
they present a very majestic appearance. They were discovered 
in the year 1609. 



ELEMENTARY ACCOUNT OF SATURN. 
LESSON XVI. 

Saturn is situated between the orbits of Jupiter and Herschel^ 
at a mean distance of 900,000,000 of miles from the sun, around 
which it revolves in about thirty of our years, its velocity being 
22,000 miles an hour. It turns on its axis in a little more than ten 
hours. 

Half a century ago, Saturn was the remotest planet from the sun 
which had been discovered ; and from its splendid appendages, it is 
still an object of intense interest to the scientific observer. It is 
represented by this character, (>2,) denoting an old man supporting 
himself upon a staff. The same character is also used to denote 
lead among metals. 

Saturn receives about one ninetieth part of the light enjoyed at 
the earth. Its density is about one half the density of water, mak- 
ing about one hundred times as much matter, and more than one 
thousand times as much bulk in Saturn, as in the earth. At the 
equator of this planet, there are in one of its years not less than 
25,000 days. 

When viewed through a good telescope, Saturn exhibits a beau- 
tiful appearance, being decorated with various belts, interspersed 
with spots, and encompassed by a bright luminous double ring, 
which very much resembles the wooden horizon of an artificial 
globe. This ring was discovered by Galileo, in 1609. 



21. How many moons has Jupiter? 22, When were they dis- 
covered ? 

1. How far from the sun is Saturn ? 2. In what time does it revolve ? 

3. What is its velocity ? 4. In what time does it turn on its axis ? 

5. What does the character representing this planet denote ? 6. How 

does the solar light at Saturn compare with what is experienced at the earth ? 

7. What is the density of Saturn ? 8. How does it compare with the 

earth in quantity of matter and bulk ? 9. How many days are in one of 

its years ? 10. How does Saturn appear viewed through a good telescope ? 

11. When and by whom was the ring of Saturn discovered? 



32 FIRST BOOK IN ASTRONOMY. 

The ring casts a deep shadow on that part of the body of Satufft, 
which is opposite the sun. Each half of the planet in succession 
must be involved in this dark shadow, during one half of the planet's 
annual revolution, almost fifteen of our years. For the same term, 
each, in succession, must enjoy the light of the double ring, a light 
more brilliant than that of the planet itself. 

The distance between Saturn and his inner ring, is more than 
20,000 miles; and between the inner and the outer ring, nearly 
3000 miles. The inner ring has a breadth of 20,000 miles, and 
the outer one, of more than 7000 miles. Thus the whole distance 
from the surface of Saturn to the most distant part of the outer ring, 
is about 50,000 miles. 

There have been various conjectures concerning the substance 
of Saturn's ring. Some have supposed it to be composed of a vast 
assemblage of planets ; others have supposed it to be a permanent 
bright cloud ; and Dr. Herschel considers it a solid body, of equal 
density with the planet. He is also of the opinion, that the edge 
of the ring is not flat, but spheroidical in its form. 

Beyond the rings of Saturn are situated seven satellites or moons 
which constantly attend the planet in its revolution about the sun. 
These satellites are unequal in size, the largest being nearly of the 
magnitude of the earth. 

The rings and moons of Saturn serve to reflect the solar light 
upon the planet, especially that part which is turned away from 
the sun. 

There is not, perhaps, says Dr. Herschel, another object in the 
heavens, that presents us with such a variety of extraordinary phe- 
nomena, as the planet Saturn ; a magnificent globe, encompassed 
by a stupendous double ring; attended by seven satellites; orna- 
mented with equatorial belts; turning upon its axis; mutually 
eclipsing its ring and satellites, and eclipsed by them ; and all the 
parts of this superb apparatus occasionally reflecting light to each 
other. 

^ 12. On what part of the body of Saturn does the ring cast a shadow ? — — 
13. For what length of time is each half the planet successively involved in 

dark shadow ? 14. What is said of the light of the ring ? 15. What is- 

the distance between Saturn and the inner ring ? 16. And between the 

inner and the outer riflg ? 17. What is the breadth of the inner ring ? 

18. What is the breadth of the outer one.' 19. What is the distance from 

the surface of Saturn to the most distant part of the outer ring .' 20. What 

conjectures have been made concerning the nature of Saturn's ring.? 

21. How many satellites has Saturn ? 22. What is said of their size ? 

23. What do the rings and moons of Saturn serve to do? 24. Wliat does- 

Dr. Herschel say of the general appearance of this planet ? 



FIRST BOOK IN ASTRONOMY. 3« 

At the top of Plate III. is a representation of Saturn, when the 
ring is very oblique to the observer. At the bottom of the same 
plate, is a representation of it as it would appear to the spectator, 
placed in a line at right angles to the plane of the ring. 



ELEMENTARY ACCOUNT OF HERSCHEL, OR URANUS. 
LESSON XVII. 

The inequalities observed in the motions of Jupiter and Saturn, 
which could not be accounted for from the mutual actions of these 
planets, led some astronomers to suppose that there existed another 
planet, beyond the orbit of Saturn, by whose action these irregular- 
ities were produced. This conjecture was confirmed in the year 
1781, when Dr. Herschel discovered the planet called after his 
own name. 

- This planet is also called the Georgium Sidus, in honor of 
George IIL the king of Great Britain, at the time of its discovery. 
It is also called Uranus, in allusion to the heathen deities, by which 
the other planets are distinguished. Thus in heathen mythology, 
Uranus was the father of Saturn ; Saturn the father of Jupiter ; and 
Jupiter the great progemtor of Mars, Venus, and Mercury. 

Herschel revolves in an orbit at the chilling distance of eighteen 
hundred millions of miles from the sun ; being about double the 
distance of Saturn. Heat and light are about three hundred and 
sixty times less than at the earth. It shines with a bluish light, 
and is seldom seen without the aid of a telescope of great magnify- 
ing power. 

The density of Herschel is equal to water. Its revolution about 
the sun is performed in about eighty-four of our years, moving at 
the rate of 15,000 miles an hour. It has not, for a certainty, been 

25. What does the figure at the top of Plate III. represent .? 26. What 

does that at the bottom of the same plate represent ? 

1. What led astronomers to suspect the existence of a planet beyond Sat- 
urn.^ 2. When was the planet Herschel discovered ? 3. By whom .^ 

4. Why is this planet called Georgium Sidus ? 5. Why is it called 

Uranus ? 6. What account is given of the origin of the names of the dif- 
ferent planets ? 7. How far distant from the sun is Herschel ? 8. How 

does this distance compare with that of Saturn ? 9. How does the degree 

of solar light and heat at Herschel compare with what is enjoyed at the 

earth ? 10. What is the color of its light? 11. Can it be seen without 

a telescope .? 12. What is the density of Herschel? 13. In what time 

is its revolution round the sun performed? 14. What the velocity of motion? 

E 



34 FIRST BOOK IN ASTRONOMY. , 

ascertained to have a rotation on its axis ; but it is supposed to 
have one, which is completed in ten or eleven hours. 

Judging from the little we know of this planet, and from our 
notions of heat and cold, it seems rational to suppose that it is alto- 
gether uninhabitable. But if the planets are really phosphorescent, 
as is conjectured ; and, if they are all furnished with internal na- 
tive heat, which seems highly probable, by these means any de- 
ficiency of the sun's light and heat can be easily supplied, even at 
Herschel. The wisdom and goodness of the Almighty are infinite ; 
and it is presumption in man to set bounds to them. It requires 
no exertion of credulity to suppose that this planet may be rendered 
as suitable to intelligent creatures for a residence as the earth. 

Herschel has six satellites; but they are so distant from us, and 
have been so recently discovered, that we know but little of the 
physical laws which govern them. Dr. Herschel, who discovered 
them, observes that they revolve round their primary at different 
distances, in different periods, with different velocities, and in orbits 
which are nearly at right angles with the ecliptic. 



DESCRIPTION OF THE MOON. 
LESSON XVIII. 

The Moon is a satellite to the earth, and partially supplies it with 
light, in the absence of the sun. It is an opaque body, in shape 
nearly globular, and in size about one fifth part of the earth. Its 
diameter is 2,180 miles; and its circumference about 6,851 miles. 
The mean distance of the Moon from the earth, is 240,000 miles ; 
and from the sun, 95,000,000 miles. 

The Moon is about twenty-nine days and a half in revolving 
round the earth, and is carried with the earth round the sun once 
a year. It turns on its axis in the same time that it performs its 
revolution round the earth. The light of the sun illuminates one 
half of its surface, and leaves the other half in darkness. 



15. In what time is it supposed to turn on its axis ? 16. What infer- 
ence might be drawn from the small amount of light and heat at Herschel ? 

17. On what ground might it be supposed that it is inhabited .? 

18. How many satellites has this planet ^ 19. Who discovered them .? 

20. What does he say of them ^ 

1, How does the moon compare with the earth in size?- 2. What is its 

diameter .? 3. Its circumference .? 4. How far is it from the earth .? 

5. In what time does it revolve round the earth.? 6. In what time does 

it turn on its axis ? 



FIRST BOOK IN ASTRONOMY. 35 

Of the illumination of the Moon we perceive different degrees, 
according to its various positions with respect to the sun and the 
earth. We see one half of its body enlightened, or a full moon, 
when it is placed in opposition to the sun, or when the sun is in 
one part of the heavens, as west, and the Moon in the opposite part, 
as east. 

When the Moon is in conjunction with the sun, or in that part of 
its orbit which is between the earth and the sun, its enlightened 
surface is turned from us, which renders it invisible ; this is the 
time of the new moon. When the Moon appears in the intermedi- 
ate parts of its orbit, between the conjunction and opposition, and 
about half its illuminated surface is turned towards us, it is in its 
quadratures. 

When more than half of its illuminated surface is turned towards 
tts, it is called gibbous ; when less than half, it is called horned. 
The conjunction and opposition of the Moon are frequently called 
syzygies. Its phases are its various appearances from the new to 
the full moon. 

As the Moon illuminates the earth by light reflected from the sun, 
so it is reciprocally illuminated by the earth, which reflects the 
sun's rays to the surface of the Moon. And, as the surface of the 
earth is more than thirteen times greater than that of the Moon, 
the earth must appear, to the inhabitants of the Moon, thirteen 
times larger than the Moon does to us. 

The rotation of the Moon on its axis being performed in the 
same time that it goes round the earth, it is plain that the inhabit- 
ants of one half of the lunar world are totally deprived of the sight 
of the earth, unless they travel to the opposite hemisphere. If the 
Moon did not complete a rotation on its axis in the same time of 
performing a revolution about the earth, it would not always in this 
monthly revolution present to us the same face. 

The dark parts of the Moon, formerly thought to be seas, are 
found to be only vast deep cavities, and places not reflecting the 

7. In what position with respect to the sun and earth do we see the moon 
when it is full ? 8. What do we mean when we say the moon is in opposi- 
tion to the sun ? 9. And when do we say it is in conjunction with the sun ? 

10. When is the moon neio ? 11. When is it in its quadratures .' 

12. When is it called gibbous ? 13. When is it horned ? 14. What are 

its syzygies ? — —15. What are its phases ? 16. By what figure are the 

phases of the moon represented.? 17. How does the earth appear at the 

moon ? 18. Is the earth seen upon every part of the moon .'' 19. How- 
do we know that the moon turns on its axis in the same time that it revolves 

round the earth .' 20. What were the dark parts of the mo»n formerly 

supposed to be ^ 21. What are they ? 



36 FIRST BOOK IN ASTRONOMY. 

sun's light. Some of these excavations are thought to be four miles 
in depth, and forty in width. A high ridge generally surrounds 
them, and often a mountain is seen, by the aid of a telescope, to 
rise in the centre. These immense depressions probably very much 
resemble what would be the appearance of the earth at the Moon, 
were all the seas and lakes dried up. 

Several of the lunar mountains have been estimated to be four or 
five miles in height. It is also conjectured that the Moon has ex- 
tensive volcanoes. One of them was particularly described by Dr. 
Herschel. He says it exactly resembled a small piece of burning 
charcoal, when it is covered with a thin coat of white ashes ; and 
that its brightness was equal to that with which such a coal would 
be seen to glow by faint day light. 

That the spots in the Moon, which are taken for mountains and 
valleys, are in reality such, is evident from their shadows ; for in 
all situations of this luminary, the mountains or elevated parts cast 
a triangular shadow in a direction opposite to that of the sun. The 
cavities or hollows, on the contrary, are always dark on the side 
next the sun, and are illuminated on the opposite side. 

If the surface of the Moon were smooth and polished like a mir- 
ror, or covered with water, it would never reflect the rays of the sun 
in the copious manner they are now diffused ; but in some positions 
would show us the image of that luminary not larger than a point, 
with such a lustre as tobe hurtful to the organs of vision. 

The difference between the rising of the Moon on one day and 
the preceding is generally about fifty minutes. But in places of 
considerable latitude, there is a remarkable difference about the 
time of harvest, when at the season of full moon it rises several 
nights together only about twenty minutes later on the one day 
than on that immediately preceding. 

By thus succeeding the sun before the twilight is ended, the 
Moon prolongs the light, to the great benefit of those who are en- 
gaged in gathering in the fruits of the earth ; and hence the full 
moon at this season of the year is called the Harvest Moon. It is 



22. Of what depth and extent are some of these cavities ? 23. By what 

are they surrounded ? 24. What do they resemble ? 25. Of what height 

are some of the lunar mountains.? 26. What is conjectured of the lunar 

mountains ? 27. How did Dr. Herschel describe one of them.'' 28. How 

is it evident that there are mountains and valleys in the moon ? 29. How 

would the rays of the sun be reflected by the moon, if the surface of it were 

smooth and polished like a mirror ? 30. What is the difference between 

the rising of the moon from one day to another .? 31. With what excep- 
tion is this ? 32. What advantage results from this .' 33. What is the 

full moon at this season of the year called ? 



'W^'^r J^KM WVIUL 'MmOM 



FT.ATF.V 



M^^I 



Wi 




i^ %: 



%^ ^. 



0:felt^n J. 



FIRST BOOK IN ASTRONOMY. 37 

believed that this was observed by persons engaged in agriculture, 
at a much earlier period than it was noticed by astronomers. This 
phenomenon is occasioned by the Moon's orbit lying sometimes 
more oblique than at others. 

The light of the Moon, condensed by the best mirror, produces 
no sensible heat upon the thermometer. The quantity of light 
which falls on the hemisphere of a full moon is so rarefied before 
it reaches us, that it would require, according to the calculation of 
Dr. Hooke, more than 100,000 full moons to give a light and heat 
equal to that of the sun at noon. 

The seasons of the Moon are subject to about one fourth part of 
the variety which ours experience ; from this it might be inferred, 
that they are mild and considerably uniform. But the day and 
night being each equal to about fifteen of our days, together with the 
conclusion that there is no water on its surface, seem to be strong 
arguments against the Moon's being a habitable globe. However, 
if the Moon be inhabited, the Creator has undoubtedly fitted the 
inhabitants to the situation which they occupy. 

Among many of the heathens of antiquity, the Moon was an ob- 
ject of stated worship. The new moons were particularly ob- 
served by the Israelites as the times of their festivals. The feast 
of the new moon was held on the first, or the first and second days 
of theif month. The period of time between one new moon and 
another, was called a moon. They reckoned their time by moons, 
and it is probable that this was the first division of time. The term 
month, is evidently derived from the word moon. Twelve moons 
are very nearly equal to one revolution of the earth round the sun. 

Telescopic views of the new and full moons, may be examined 
in figures 1 and 2, of Plate V. In figure 3, of Plate VII. may be 
examined the several phases of the Moon, as presented to the earth 
in its revolution about that planet. 



34. By whom was this phenomenon first discovered ? 35. By what is it 

occasioned ? 36. Can heat be produced by the condensed light of the 

moon.? 37. What comparison is made between the light of the sun and 

moon ? 38. What is said of the seasons of the moon ? 39. What cir- 
cumstances are against the idea that the moon is inhabited ? 40. How 

did the heathens of antiquity view the moon? 41. What regard had the 

Israelites to the moon, connected with their religious rites? 42. How did 

they reckon their time ? 43. From what is the term probably derived ? 

44. What is represented by figures 1 and 2, of Plate V. ? 45. What is 

represented by figure 3, of Plate VII. ? 46. How is the moon represented 

■at A, in that figure? 47. How is it represented at E ? 48. How is it 

represented at C ? 49. How is it represented at B and F ? 50. How is 

it represented at D and I ? 



3S FIRST BOOK IN ASTRONOMY. 

AN ACCOUNT OF COMETS. 
LESSON XIX. 

Comets are planetary bodies moving in very elliptical orbits, 
sometimes approaching so near the sun as to be within the orbit of 
Mercury, and, at other times, receding so far from it, as to be 
greatly beyond the known boundary of the solar system. They 
appear in every region of the heavens, and move in every possible 
direction. 

Comets are distinguished by a lucid train or tail, issuing from 
that side which is turned away from the sun. The train is so 
transparent that the fixed stars may be seen through it ; and some- 
times it extends to an immense distance in the heavens. The far- 
ther it reaches, the broader it seems to become, and at times it is 
divided into rays. 

In a clear sky, the solid body of a comet often reflects a splendid 
light. If viewed through a telescope it appears full of spots and 
inequalities. Sir Isaac Newton supposed that the tail of a comet 
was caused by a thin vapor, which was raised in consequence of 
the intense heat it received from the sun. 

Comets were formerly considered as supernatural agents, sent by 
the Almighty, as omens of plagues, famines, pestilences, and other 
scourges of mankind, for their sins. The comet of 1456 was view- 
ed with feelings of horror. Its long train spread consternation over 
all Europe, already terrified at the success of the Turkish arms, 
which had just destroyed the great empire. Pope Callixtus, on this 
occasion, ordered a prayer, in which the comet and the Turks 
were included in the same anathema. 

Modern discoveries in astronomy have proved that all such fears 
were groundless; that comets are governed by laws similar to those 
which govern the planets. No doubt the all-wise Creator of the 
universe formed these bodies for benevolent purposes, although 
most of these purposes must be unknown to us, or deduced only 
by reasoning from analogy. 

1. What are comets ? 2. What is said of their orbits ? 3. By what 

are comets distinguished ? 4. What is said of the transparency of this 

train ? 5. How does it appear when viewed by a telescope ? 6. By 

what did Sir Isaac Newton suppose the train was caused? 7. How were 

comets formerly considered ? 8. What is said of the one in 1456 ? 

9. And of Pope Callixtus in relation to it ? 10. What do modern discov- 
eries prove in relation to comets? 11. What is said of the purposes of the 

Deity in relation to their formation ? 



FIRST BOOK IN ASTRONOMY. 39 

It is not to be presumed that he would hurl worlds at random 
through the immensity of space, or permit any portion of his works 
to be affected injuriously by fortuitous circumstances. Religion 
glories in the test of reason, of knowledge, and of tiue wisdom ; it is 
everywhere connected with, and elucidated by them. From phil- 
osophy we may learn that the more his works are contemplated, 
the more he must be adored ; and the more evinced his govern- 
ment and superintendance over every portion of his works. 

Tycho Brahe, a Danish astronomer, was the first who restored 
comets to their true rank in the creation, by assigning them their 
situation in the solar system. 

The number of comets belonging to the solar system is unknown. 
More than five hundred since the Christian era have been observ- 
ed. The orbits of ninety-six comets, up to the year 1808, have 
been calculated ; but of all these, the periodical returns of three 
only are known, with any degree of certainty. One of these re- 
turns at intervals of seventy-five years; one, at intervals of one 
hundred and twenty-nine years ; and the other, at intervals of five 
hundred and seventy-five years. Of these, that which appeared in 
1680 is the most remarkable. 

Sir Isaac Newton calculated the heat of this comet, when near- 
est the sun, to be 2000 times greater than that of red hot iron. He 
also calculated that its heat must be retained a very long time. 
Supposing it to have been as large as our earth, and that it had the 
property of cooling 100 times faster than red hot iron, he states 
that it would take the comet 500 years to lose the heat it had ac- 
quired from the sun. 

As comets have but a feeble action on other bodies, it is conclud- 
ed that they contain but a small quantity of matter. This may be 
illustrated by the comet of 1454, which is said to have eclipsed the 
moon, so that it must have been very near the earth. Yet it pro- 



12. What are we not to presume in relation to them ? 13. In what does 

religion glory ? 14. From philosophy what may we learn .'' 15. Who 

first assigned to comets their proper place in the solar system ? 16. How 

many comets have been observed since the Christian era ? 17. To the or- 
bits of how many have calculations been applied ? 18. What are the 

periodical returns of the three which have been determined ? 19. Which 

one is the most remarkable? 20. What was the heat of that comet.' 

21. How long time did Sir Isaac Newton suppose it would retain its heat.' 

22. What is said of the quantity of matter which comets contain .'' 

23. What is said of the comet of 1454, in illustration of this ? 



40 FIRST BOOK IN ASTROiXOMY. 

duced no sensible effect on the earth's motions. The comets of 
1472 and 1760, also came very near the earth ; yet their attractions 
produced no sensible effect on the earth's motions. Also the com- 
et of 1770, came very near the satellites of Jupiter, but produced 
no derangement in the system. 



THEORY OF FIXED STARS. 
LESSON XX. 



The universe, so far as human observation has extended, con- 
sists of infinite or boundless space, in which are numberless fixed 
stars, of the nature, bulk, and properties of the sun ; but because 
they are at such immense distances from the earth, they appear to 
our eyes only as so many beautiful shining points. They are call- 
ed fixed stars, because they do not change, like the planets, their 
relative position ; and they are distinguished from the planets by 
their twinkling light. 

It is supposed that the fixed stars have primary and secondary 
planets revolving round them, as the planets of our system revolve 
round the sun. Were the sun as far from us as these stars are, 
it would doubtless appear as they now do. It is certain that they 
do not reflect the sun's light as do the planets ; for their distance 
is so great, that they would not, in that case, be visible. 

All the fixed stars, with the exception of the polar or north star, 
notwithstanding they do not change their relative position, appear 
to have a motion like the sun and moon, rising in the east, in- 
creasing in altitude until they approach the meridian, and declining 
to the western horizon, where they disappear. This apparent mo- 
tion is caused by the revolution of the earth on its axis from west 
to east. 



24. What ig said of those comets which appeared in 1472, 1760, 
and 1770? 

1. Of what does the universe consist? 2. Why do they appear so 

small ? 3. Why are they called fixed stars ? 4. How are they distin- 
guished from the planets ? 5. What is supposed of them ? 6. Under 

what circumstances would our sun appear like one of them ? 7. How is 

it known that the fixed stars do not reflect the sun's light?- 8. What mo- 
tion do the fixed stars appear to have ? 9. By what is this apparent mo- 
tion caused ? 



FIRST BOOK IN ASTRONOMY. 41 

The immoveable appearance of the polar star is occasioned by 
the axis of the earth pointing directly to it. Its elevation above 
the horizon of any place is always equal to the latitude of that place, 
or its nearest distance to the equator. 

The number of fixed stars visible to the naked eye, in either 
hemisphere, is not more than a thousand. They seem indeed to 
be innumerable, when, in a clear winter's evening, we turn our 
eyes towards the heavens. But by looking attentively, we shall find 
that most of those bright spots, which appeared to be stars, vanish 
from our view. This illusion is owing to the twinkling light with 
which the fixed stars are seen ; and, to our viewing them confus- 
edly, and not reducing them to any order. 

By the aid of a telescope we are enabled to discover myriads of 
stars, which were before invisible to the unassisted eye ; and, as 
we increase the power of the instrument, more and more stars are 
brought into view, so that the number may be considered infinite. 
Dr. Herschel was enabled, in one quarter of an hour, to count one 
hundred and sixteen thousand, which passed through the space 
embraced by his powerful glass. 

Many stars, which to an observer unaided by instruments appear 
single, are found, on being examined by a telescope, to consist of 
two, and sometimes of three or more stars. Dr. Herschel discov- 
ered four hundred of this description. Other astronomers have 
discovered a much greater number. 

Upon viewing the heavens during a clear night, we discover a 
pale irregular light, and a number of stars whose mingled rays form 
the luminous tract called the milJxy way. The stars themselves 
are at too great a distance to be perceived by the naked eye ; and 
among those which are visible with a good telescope there are 
spaces apparently filled with others in immense numbers Many 
whitish spots or tracts, called nehulcc, are visible in different parts 
of the heavens, which are supposed to be milky w^ays at an incon- 
ceivable distance. 



10. Why does not the pole star have this apparent motion ? 11. What 

elevation above the horizon has this star ? 12. How many fixed stars can 

be seen by the naked eye ? 13. How do tliey appear as to number? ■ 

14. Why do they appear more numerous than they are .' 15. What is 

said of the number seen by a telescope .? IG. How many did Dt. Herschel 

count, in a given time and place? 17. How do some stars, appearing to 

the naked eye single, appear when viewed through a telescope ? 18. How 

many of these have been discovered? 19. What forms the milky way? 

20. How does the milky way appear viewed through a telescope.'—— 

21. What are nebulae ? 

F 



42 FIRST BOOK IN ASTRONOMY. 

The magnitudes of the fixed stars appear to be different from one 
another, which difference may arise either from a diversity in their 
real magnitudes, or distances ; or from both these causes acting to- 
gether. The difference in the apparent magnitude of the stars is 
such as to admit oi their being divided into six classes. The 
largest are called stars of the first magnitude, and the least which 
are visible to the naked eye, stars of the sixth magnitude. Stars 
that cannot be seen without the help of glasses are called telescopic 
stars. 

Some stars are subject to periodical variations in apparent mag- 
nitude; at one time being of the second, or third, and at another, 
of the fifth or sixth. Some have alternately been noticed to appear 
and disappear ; being visible for several months, and again invisible. 
Several stars mentioned by ancient astronomers are not now to be 
found ; and some are now observed, which are not mentioned in 
the ancient catalogues. 

It is conjectured that the fixed stars are at such an immense dis- 
tance, that light, which moves at the rate of 100,000 miles per sec- 
ond, would be nearly one year and a quarter in passing from the 
nearest fixed star to the earth; and a cannon ball discharged from 
a twenty-four pounder with a velocity of nineteen miles a minute,, 
would be seven hundred and sixty thousand years passing from the 
nearest star. Sound, which moves at the rate of thirteen miles a 
minute, would be about one million, one hundred and twenty eight 
thousand years in passing through the same space. 

Dr. Herschel has calculated that the distance of the remotest 
nebulae, exceeds that of the nearest fixed star at least three hun- 
dred thousand times. Upon this fact, he thus remarks ; that from 
facts well known, it might be proved, the rays of light, which enter 
the eye from the star Sirius, cannot have been less than six years 
and four months and a half in their passage to the observer. 
Hence, he says, it follows that when we see an object at a calcu- 
lated distance, at which one of these very remote nebulae may still 



22, "Why do the fixed stars appear to be of different magnitudes ?- 

23. Into how many classes are they divided? 24. What ones are called 

telescopic stars? 25. To what periodical variations are some of the fixed 

stars subject? 26. What difference is there between the ancient and mod- 
ern catalogues of stars ? 27. What calculation has been made, as to the 

distance of the nearest fixed star, by the circulation of light ?- 28. How is 

this distance illustrated by a cannon ball ? 29. And by sound ? 30. What 

calculation has Dr. Herschel made of the. distance of the most remote nebu- 

IsB ? 31. What does he say of the time Vvhich light occupies in coming 

from the star Sirius to the earth? 



FIRST BOOK IN ASTRONOMY. 43 

be perceived, the rays of light which convey its image to the eye, 
must have been almost two millions of years on their way; and 
that consequently so many years ago, this object must already have 
had an existence in the sidereal heavens, in order to send out those 
rays by which we now perceive it. 

But when we hare reached the utmost distance to which the 
power of our instruments can penetrate, who will say, that we are 
approaching any limits of the creation 1 Who will say that if the 
disembodied spirit should travel forward through eternity, number- 
less systems would not be continually spreading before it 1 

We caimot contemplate the fixed stars without exclaiming. How 
inconceivably great and wise and good is the Being who made, 
governs, and sustains them ! We behold not one world only, but a 
system of worlds, regulated and kept in motion by the sun ; not one 
sun and one system only, but millions of suns and systems, multi- 
plied without end, perpetually submissive to the laws which govern 
them. Such a view of the material creation may well induce us to 
adopt, as our own, the language of the royal Psalmist of Israel, and 
say — *' When I consider thy heavens, the work of thy fingers, 
the moon and the stars which thou hast ordained ; what is man, 
that thou art mindful of him ? or the son of man, that thou visitest 
him V 



THE ZODIAC AND THE TWELVE SIGNS. 
LESSON XXI. 

The Zodiac is an imaginary belt round the heavens, among 
the fixed stars, sixteen degrees wide, the centre of which is the 
plane of the ecliptic. In this space or belt all the primary planets 
revolve round the sun, with the exception of Juno, Pallas, and 
Ceres, three of the asteroids. 

The ecliptic, and consequently the Zodiac, has been divided into 
twelve equal parts, consisting of thirty decrees each, called signs. 
As one half of the ecliptic is situated north of the equator, and 

32. What inference does he hence draw of the distance of the nebulse from 

us? 33. Is it to be supposed that the most distant nebulae are the boundaries 

of the material universe ? 34. How does a contemplation of the fixed stars 

impress us with regard to the Supreme Being ? 35. With what quotation 

from Scripture is the lesson concluded? 

1. What is the zodiac ? 2. Within this space which of the planets re- 

volve? 3. Which ones do not revolve in it? 4. How has the ecliptio 

been divided ? 



44 FIRST BOOK IN ASTRONOMY. 

the other half south of it, so six of these signs are in the north equa- 
torial hemisphere, and the other six in the southern hemisphere* 

These signs are fanciful, but refer to the business of the season 
which they represent. Their names are, Aries T, the Ram ; Tau- 
rus 8 , the Bull ; Gemini n, the Twins; Cancer G, the Crab ; 
Leo Sli the Lion ; Virgo n^, the Virgin ; Libra rfi, the Balance ; 
Scorpio H]., the Scorpion ; Sagittarius / , the Archer ; Capricor- 
nus Vf , the Goat ; Aquarius «. , the Water Bearer ; and Pisces H , 
the Fishes. The first six are northern signs, and the latter six 
are southern signs. 

The sun enters the sign, Aries, on the 21st of March ; Taurus, 
the 19th of April; Gemini, the 20th of May; Cancer, the 21st of 
June ; Leo, the 22d of July ; Virgo, the 22d of August; Libra, 
the 23d of September ; Scorpio, the 23d of October ; Sagittarius, 
the22d of November; Capricornus, the 21st of December; Aqui- 
rius, the 20th of January; and Pisces, the 19th of February. 

The names of the twelve signs are the same as of the twelve con- 
stellations situated within the zodiac. The constellations formerly 
were in the same places of the signs, to which they respectively 
gave names ; but the zodiac being immoveable, and the stars hav- 
ing a motion from west to east, the constellations do not now cor- 
respond to their proper signs. Hence arises what is called the 
precession of the equinoxes. This change amounts to a sign in 
2150 years ; and in 25,791 years the whole circle will be complet- 
ed, producing a perfect correspondence between the signs and 
constellations. 

There is sometimes observed in the zodiac, a brightness resem- 
bling that of the galaxy or milky way. It appears at certain seasons 
of the year, in the morning before sunrise, and at evening after 
the setting of that luminary. About the first of March, at 7 o'clock 
in the evening is the best time for observing it. According to 
Foulqueit, it is to be seen at all seasons of the year, at Gaudaloupe, 

5. How many of these signs are north, and how many south of the equa- 
tor ? 6. What are their names ? 7. Which ones are the northern signs ? 

8. Which ones are the southern signs ? 9. At what times in the year 

does the sun enter these signs respectively ? 10. From what do these 

Bigns derive their names ? 11. Do the constelhitions correspond with the 

pigns as to situation ? 12. Why do they not correspond ? 13. How 

many years does it require to produce a variation of one sign ? 14. And 

how many years to produce an entire circle of change ? 15. When 

this circle is completed, how will the signs and constellations be in 

relation to each other .? IG. What is sometimes observed in the zodiac .? 

• 17.^ What is it called? 18. At what hours may it be seen .? 19. 

When is the best time for observing it ? 20. What does Foulquier say of 

it.? 



FIRST BOOK IN AST5LONOMY. 45 

when the weather admits. Since the time of Cassini, in the year 
1693, by whom it was particularly observed, it has been called 
Zodiacal Light. Previous to that period, it did not attract much 
notice. 



HISTORY OF THE CONSTELLATIONS. 
LESSON XXII. 

As soon as astronomy begun to be studied, it must have been 
found necessary to divide the heavens into separate portions, and 
to givo each some name and representation, in order that astrono- 
mers, in speaking of the stars, might be understood. Accordingly 
we find that at a very early period of the world, the visible heavens 
were separated into constellations or collections of stars. Those 
called Orion, Arcturus, and the Pleiades, are mentioned in the 
book of Job; and, in other ancient books, there are references to 
the same subject. 

The sections of the sky or clusters of stars, when first made, 
were represented by the ancients under the outlines of natural ob- 
jects, or of certain imaginary figures suggested to them by their own 
fancy, or else by the actual disposition of the stars themselves, which 
in some instances is very striking. Thus we have obvious represen- 
tations of crosses and triangles ; the Northern Crown, or Corona 
Borealis bears a strong resemblance to a wreath or garland; and 
the head of the Bull, or Taurus, is known under the same name by 
different nations, who probably never had, at the time of its inven- 
tion, any intercourse with each other. Even our Indians who wan- 
der near the banks of the Missouri call it the Deer's Head. This 
analogy, however, in most cases is exceedingly faint and imperfect. 

As a specimen of what ingenuity can accomplish, when aided 
by an active imagination, an account will here be given of the 
characters which denote the signs or constellations in the zodiac, 
These are thought to be less arbitrary tlian those in the other parts 



21. By whom and when was it first particularly observed ? 

1. Whence was the necessity for dividing the heavens into constellations.' 

—2. What are constellations ? 3. What ones are named in the book of 

Job.'' 4. How were the constellations at first represented.' 5. What 

is said of the Northern Crown? 6. And of the constellation Taurus .' — -« 

7. Which constellations are to be particularly described .' 



46 FIRST BOOK IN ASTRONONY. 

of the heavens. The animals by which they are denoted are 
Chaldean or Egyptian hieroglyphics ; and were perhaps designed 
as emblems of the different productions of nature, in those seasons 
over which they preside, or else represented some remarkable occur- 
rence in each month. 

Thus, the spring signs, Aries, Taurus, and Gemini, were distin- 
guished for the production of such animals as were held in the 
highest esteem ; the third month, being the most abundant, was 
represented by Gemini. When the sun enters the fourth sign, it 
retrogrades, or begins to return towards the south pole, which mo- 
tion is represented by Cancer, or the Crab, which often runs back- 
wards. The heat which usually follows in the next month is de- 
noted by the Lion, an animal remarkable for its fierceness, and 
which at this season, impelled by thirst, leaves the desert, and visits 
the banks of the Nile. 

About the time of harvest the sun enters the sixth sign, and this 
season was characterized by a Virgin, or female reaper, bearing an 
ear of corn. When the sun enters Libra, the days and nights are 
equal all over the world, and seem to observe an equilibrium, like 
a balance. Autumn, which produces fruit, brings with it a variety 
of diseases, and this season is denoted by the venomous Scorpion, 
which is thought to wound with its sting as it receded. The fall 
of the leaf was the season for hunting, and the stars, which mark- 
ed the sun's path at this, time, were aptly represented by a hunts- 
man or archer. 

The Goat, which delights in clambering, is the emblem of the 
winter solstice, when the sun begins to ascend from the southern 
tropic, and gradually to increase in height for the ensuing half year. 
Aquarius is represented by the figure of a man pouring out water 
from an urn, an emblem of the rainy and uncomfortable season of 
winter. The Fish, or twelfth and last old zodiacal sign, denoted 
the fishing season. The severity of winter being over, and the 
flocks not affording sustenance, the seas and rivers were then open 
and abounded with fish. 

The number of constellations is now ninety-two ; of which twelve 
are in the zodiac ; thirty-five are in the northern hemisphere ; and 

8. By what are these denoted? 9. And for what might they have been 

designed? 10. Which are the spring signs? 11. How are they ex- 
plained ? 12. How is Cancer explained ? 13. How is the Lion ? 14. 

How is Virgo ? 15. How is Libra ? 16. How is the Scorpion ? 

17. How is the Archer ? 18. How is the Goat ? 19. How is Aquarius ? 

20. How are the Fishes? 21. What is the present number of constel- 

lations ? 22. How are they distributed in the heavens ? 



FIRST BOOK IN ASTRONOMY. 47 

forty-five in the southern hemisphere. The ancient constellations, 
including those in the zodiac, vvere only forty-eight in number. 
As it is not very probable that the ancients crossed the equator, 
they never could have seen the stars in the south polar circle ; and 
it therefore remained for modern astronomers to group the stars in 
that portion of the heavens. The ancients likewise often left spaces 
in the sky, between their groups, filled with w^hat they call unformed 
stars, some of which have since been arranged into constellations; 
so that at present we have represented on our celestial charts the 
number above given. 

The heavens being thus divided, it is comparatively an easy task 
to number and name the stars which compose each group. By this 
means the astronomer becomes as familiar with the heavens, as the 
geographer is with the earth. The former can as readily refer to 
the place of any particular constellations or to the several stars 
which compose them, as the latter can, on a map of the world, to 
any particular country, or to the cities which are found in it. 



SHOOTING STARS, OR METEORS. 
LESSON XXIII. 

The luminous appearances, known by the name of shooting stars, 
are too common not to have been seen by most of the persons for whom 
this book is designed. But as frequent as they are, the phenomenon 
is not well understood. Some imagine that they are occasioned by 
electricity, and others that they are nothing but luminous gas, per- 
haps phosphuretted hydrogen. Others have again supposed, that 
some of them are luminous bodies which accompany our planet in 
its revolution about the sun, and that their return to certain places 
might be calculated with as much certainty and exactness as that 
of any of the comets. 

Signior Baccaria supposed they are occasioned by electricity. 
His opinion is confirmed by tire following observations. About an 
hour after sunset, he and some friends that were with him observed 

23. How many constellations did the- ancients count? 24. Why did 

they not form them in the south polar circle ? 25. What did they calf 

unibrmed stars .' 26. Is it an easy or a difficult task to become acquainted 

with the stars ? 27. What comparison is made to illustrate the ease with 

which it may be done ? 

]. Is the phenomena of shooting stars well understood.' 2. To what 

have they by different persons been ascribed ^ 3. How did Baccaria sup- 
pose they were occasioned.' 4. What account is given of one which he 

observed .' 



48 FIRST BOOK IN ASTRONOMY. 

a falling star, directing its course directly towards them, and appar- 
ently growing larger and larger, but just before it reached them it 
disappeared. On vanishing, their faces, hands, and clothes, with 
the earth and all the neighboring objects, became suddenly illumi- 
nated with a diffused and lambent light. It was attended with no 
noise. During their surprise at this appearance, a servant informed 
them, that he had seen a light shine suddenly in the garden, and 
especially upon the streams which he was throwing to water it. 

Baccaria also observed a quantity of electric matter collect 
around his kite, which had very much the appearance of a falling 
star. Sometimes hg saw a kind of halo accompanying the kite, as 
it changed its place, leaving some glimmering of light in the place 
it had quitted. 

Shooting stars have been supposed by those meterologists who 
refer them to electricity or luminous gas, to prognosticate altera- 
tions in the weather, such as rain, wind, &c. The duration of the 
brilliant track which they leave behind them, in their motion 
through the air, will be found to be longer or shorter, according as 
watery vapor abounds in the atmosphere. 

On the 12th of November, 1799, there was seen a very remark- 
able exhibition of shooting stars, at Cumana, in South America, 
and over most of the West India Islands. The following account 
of it is from the pen of a gentleman who witnessed it. He says, 
*' I was called up about three o'clock in the morning, to see the 
shooting of stars, as it is called. The phenomenon was grand and 
awful. The whole heavens appeared as if illuminated with sky 
rockets, which disappeared only by the light of the sun after day- 
break. These meteors appeared as numerous as the stars, flying 
in all possible directions except from the earth, towards which they 
all inclined more or less, and some of them descended perpendicu- 
larly over the vessel we were in, so that I was in constant expecta- 
tion of their falling on us." 

About thirty years previous to this time, a similar phenomenon 
was observed on the table land of the'Andes. At duito, there was 
seen in one part of the sky, above the volcano of Gayamba, so 
great a number of falling stars, that the mountain was thought to 
be in flames. This extraordinary light lasted more than an hour. 

5. What else did he observe, which confirmed him in the opinion that they 

are occasioned by electricity ? C. What is it supposed that they prognostic 

cate ? 7. Who suppose this ? 8. When and where was there a very 

remarkable scene of shooting stars observed ? 9. How is it described ? • 

10. When and where had there been witnessed a similar phenomenon?- 

11. What is said of this one ? 



FIRST BOOK IN ASTRONOMY. 49 

Those meteors which are heard to burst, the explosion being fol- 
lowed, as is sometimes the case, by the fall of stones, are called 
Aerolites. These stones often descend with such force as to 
bury themselves several feet in the earth. Many attempts have 
been made to account for the formation and ignition of these grand 
objects; but the subject still remains enveloped in mystery. 

It has been said that the stones, thus incontestibly proved by dif- 
ferent authorities, and from various places, to have fallen after the 
explosion of meteors, are heated and luminous when they reach 
the earth, and they have been seen in Europe, Asia, and America. 
The stones are of different sizes, and from a few ounces in weight 
to several tons. They are generally of a circular form, and covered 
with a rough black crust. Meteoric stones have been subjected to 
chemical analysis, and are found to be entirely different from all 
known stones belonging to the earth. 

The most remarkable of these meteors, so recently seen, were 
those of 1783, and 1805. The former was very luminous, and its 
diameter was estimated to be a thousand yards. The latter passed 
vv^ith such astonishing rapidity, that amazement had not subsided 
ere it vanished ; consequently, but very little dependance can be 
placed on what has been said concerning its bulk and shape. The 
light which it emitted was a pale blue, and almost as instantaneous 
as a flash of lightning, and the rushing of the enormous body pro- 
duced a sound like very distant thunder. 



AURORA BOREALIS AND HALOS. 

LESSON XXIV. 

We often see in the north, near the horizon, usually a short time 
after sunset, a dark segment of a circle, surrounded by a brilliant 
arch of white or fiery light; and this arch is often separated into 
several concentric arches, leaving; the dark segment visible between 



12. What are Aerolites ? 13. What is said of the force with which me- 
teoric stones descend to the earth ? 14. Is the theory of them understood ? 

15. In what parts of the world have they fallen .' 16. What is said of 

their sizes?* 17. Do they resemble the stones of our globe ? 18. What 

are the most remarkable meteors named ? 19. How is the first described? 

20. How is that of 1805 described .' 

G 



50 FIRST BOOK IN ASTRONOMY. 

them. From these arches, and from the dark segment itself, iii 
high latitudes, columns of light, of the most variegated and beauti- 
ful colors, shoot up towards the zenith; and sometimes masses, 
like sheaves of light. 

This phenomenon is called the Aurora Borealis, or northern 
light. It is supposed by some to be occasioned by the combustion 
of inflammable air, ignited by electricity. This kind of air is very 
light, and floats in the extreme regions of the atmosphere. By oth- 
ers, it is supposed that the Aurora Borealis is caused by the circu- 
lation of the electric fluid, from the poles of the earth to the equator. 

The Aurora Borealis is chiefly visible in the winter season, and 
in cold weather. It never appears near the equator, but of late 
years has frequently been seen towards the south pole. In the arc- 
tic regions these lights afford important relief to the gloom of the 
long winter nights. A very brilliant one is mentioned to have been 
visible in November, 1554, from the west of Ireland to the confines 
of Russia, extending over at least thirty degrees of longitude, and 
from about the fiftieth degree of north latitude, over almost all the 
northern part of Europe. In every place, it exhibited, at the same 
time, the same wonderful features. 

In serene weather, we often observe a circular light, or luminous 
ring surrounding the moon, which is called a Halo, or crown. Its 
outline sometimes faintly shows the colors of the rainbow. The 
moon is in the middle of this ring, and the intermediate space is 
generally darker than the rest of the sky. When the moon is at 
full, and considerably elevated above the horizon, the ring appears 
most luminous. It is often very large. 

We are not right in supposing that this ring really surrounds the 
moon : the true cause for such an appearance must be looked for 
in the atmosphere, the vapors of which make a refraction of the rays 
of light. False moons are sometimes seen near the real moon, and 
appear as large, but their light is paler. They are generally ac- 



1. How is the Aurora Borealis described? 2. "What is the first supposi- 
tion here named, as to the occasion of it ?■ 3. What is the second one ? 

4. At what times is it mostly visible? 5. Does the Aurora Borealis ever 

appear near the equator ? 6. Has any thing like it been seen near the south 

pole? 7. Of what use are these lights in arctic regions? 8. What is said 

of the very brilliant one in November, 1554? 9. What is a halo ? 

10. When do we see it? 11. What colors does it exhibit.^ 12. When 

does it appear most luminous ? 13. Does this ring really surround the 

moon ? 14. What then is the cause of such an appearance .'' 15. How 

are false moons, as they are called, described ? 



FIRST BOOK IN ASTRONOMY. 51 

companied by circles, some of which have the same colors as the 
rainbow, whilst others are white, and others have luminous tails. 
All these appearances are produced by refraction. The rays of 
light falling from the moon upon aqueous, and sometimes frozen 
vapors, are refracted in various ways ; the colored rays are separat- 
ed, and reaching the eye, present a new image of the moon. 

Halos, or luminous circles, also appear round the sun, and even 
round the stars, as well as round the moon. Those round the sun 
are sometimes accompanied by parhelia, or Mock Suns, as they 
are termed. 



THE ATTRACTION OF GRAVITATION, 
LESSON XXV. 

By attraction is meant that property in bodies which gives them 
a tendency to approach each other. There are several kinds of 
attraction. Thus, the magnet attracts the needle ; this is called 
the attraction of magnetism. Thus, a feather, suspended near the 
electric conducter, is attracted by it ; this is called the attraction 
of electricity. And that property which connects or firmly unites 
the different particles of matter of which a body is composed, is 
denominated the attraction of cohesion. 

The attraction of gravitation is the power by which different 
bodies tend towards each other ; and this attraction or ten- 
dency towards each other, is in proportion to the quantity of 
matter they contain. The tendency which bodies have to fall, is 
produced entirely by the attraction of the earth ; for the earth is so 
much larger than any body on its surface, that it forces every body, 
which is not supported, to fall upon it. If a brick fall from the top 
or a house, or a stone from the height in the air to which it 
is thrown, it is by the attraction of gravitation ; or the ten- 
dency which they possess to gravitate towards the centre of the 



IG. By what are they generally accompanied ? 17. How are all these 

appearances produced? 18. Are halos ever seen except round the sun? 

19. What sometimes accompany those round the sun ? 

1. What is meant by attraction ? 2. What is an instance of the attrac- 
tion of magnetism? 3. Of the attraction of electricity? 4. What is 

cohesive attraction? 5. What is the attraction of gravitation ? 6. in 

what proportion does it operate ? 7. Why do bodies tend to fall to the 

earth .' 8. What instances in illustration of this are named ? 



52 FIRST BOOK IN ASTRONOMY. 

earth. It is by the same tendency that the water of the ocean is 
kept in its place ; and that we are enabled, on ail parts of the earth, 
to stand with oar feet pointing; to the centre. 

The power of gravitation is greatest at the earth's surface, from 
whence it decreases both upwards and downwards ; but not both 
ways in the same proportion. It decreases upwards as the square 
of the distance from the centre of the earth increases ; so that at a 
double distance from the centre, above the surface, the force would 
be only one fourth of what it is at the surface. But below the sur- 
face, it decreases in the direct ratio of the distance from the centre; 
so that at the distance of half a semi-diameter from the centre, the 
force would be but half what it is at the surface. 

The attraction of gravitation and weight may be taken, in par- 
ticular cases, as synonymous terms. We say a piece of lead weighs 
a pound, or sixteen ounces; but if by any means it could be car- 
ried 4000 miles above the surface of the earth, which is about the 
distance from the surface to the centre of the earth,it would weigh only 
one fourth of a pound, or four ounces ; and if it could be transport- 
ed to 8000 miles above the earth, which is three times the distance 
between the centre and the surface, it would weigh only one ninth 
of a pound, or something less than two ounces. The same body at 
the centre of the earth would be without weight ; at 1000 miles 
from the centre, would weigh one fourth of a pound ; at 2000 miles 
from the centre, one half of a pound; at 3000 miles, three fourths 
of a pound ; and at 4000 miles, or at the surface, one pound. 

The complicated effects resulting from the existence of this prin- 
ciple in nature, were first reduced to a system by the celebrated 
Newton. One day happening to be sitting under an apple-tree, 
and an apple falling on his head, it suggested to him a variety of 
the most important reflections. Because there was motion, he 
reasoned there must be force to produce it. He was accordingly 
induced, in the first place, to investigate the phenomena of falling 



9. What is said of the ocean, and of our standing on the surface of the 

earth in illustration? 10. Where is the power of gravitation the greatest.? 

11. In what proportion does it decrease upwards? 12. And in what 

proportion downwards? 1.3. What is a synonymous term with weight ? 

14. What would be the weight of a pound of lead raised 4000 miles above 

the surface of the earth? lo. At 8000 miles above it? 16. At 1000 

miles below the surface ? 17. At 2000 miles below it .? 18. At 3000 

miles below it ? 19. At the centre ? 20. Who first reduced the princi- 
ples of gravitation to system ? 21 . What led him to reflect on the 

subject.? 22. How did he reason upon the falling of the ap- 
ple ? 



FIRST BOOK IN ASTRONOMY. 53 

bodies; but afterwards extended his researches to the heavens, and 
was enabled to comprehend the various motions in the solar system, 
which had hitherto been veiled in deep mystery. 

By the attraction of gravitation, the sun, the largest body in our 
system, attracts the earth, and all the other planets; and they, in 
turn, have a corresponding tendency to approach or gravitate towards 
the sun. And thus the moon, being smaller than the earth, gravi- 
tates towards the earth, and is attracted by it, in the same manner 
that all bodies in the vicinity of the earth are attracted by it. The 
moon would be completely drawn to the earth, and the earth and 
the other planets would be completely drawn to the sun, were it not 
that their tendency thus to gravitate, is counteracted by the centri- 
fugal or projectile force, which propels them forward in their 
orbits. It is a law of attraction, that in circular motion, the attrac- 
tion decreases as the squares of the distances from the centre in- 
crease. Any number multiplied into itself is the square of that 
number ; four being the square of two, nine the square of three, 
and sixteen the square of four. 

It is also proper to state, that bodies attract one another with force 
proportional to the quantities of matter they contain, and not with 
one proportional to their magnitudes. All bodies of equal magni- 
tude contain not equal quantities of matter. For instance, a ball 
of cork, equal in bulk to one of lead, being more porous, will not 
contain so much matter. So the sun, though more than a million 
of times as large as the earth, not being so dense and compact a 
body, contains, according to estimation, a quantity of matter only 
330,000 times as great, and hence attracts the earth with a force 
only 330,000 times more than the earth attracts that luminary. 

Hence suppose there are in a river two boats of equal bulk, at 
any distance, suppose twenty yards from each other, and that a man 
in one boat pulls a rope which is fastened to the other, the boats 
will meet in a point which is halfway between them. But if one 
boat were three times the bulk of the other, then the lighter would 
be moved three times as far as the heavier one, or fifteen yards, 
while the heavier moved only five. 

23. What is said of the sun and planets in illustration of the subject? 

24. And of the earth and moon? 25. V.Miat counteracts the tendency of 

gravitation in the planetary system ? 26. In what proportion do bodies 

gravitate towards each other ?— — 27. Do all bodies of equal magnitudes con- 
tain the same quantity of matter ? 28. What illusti ations are named ? 

29. Why does lead contain more matter than cork of the same bulk ? 

30. What comparison is made between the sun and the earth in illustration ? 

31. What is the first illustration of the two boats ' 32. What is the 

second supposition ? 



54 FIRST BOOK IN ASTRONOMY. 

ATTRACTIVE AND PROJECTILE FORCES. 
LESSON XXVI. 

As menlioned in the preceding lesson, the sun, being so immense 
a body, would, by the power of attraction, draw all the planets to it, 
unless counteracted by another force. The manner in which this 
is done is explained in Lesson VII, and by reference to figure 3, in 
Plate VI. The force of gravitation in the sun is counteracted or 
balanced by the force of projection, or the power which impels or 
revolves bodies forward in their orbits. The joint action of these 
two forces retains the planets in theirorbits ; the primaries around 
the sun, and the secondaries around their primaries. 

If the attractive power of the sun were uniformly the same in- 
every part of their orbits, they would be true circles, as seen in that 
figure, and the planets vi'^ould pass over equal portions in equal 
times; but the attractive ^owerofthe sun is not uniformly the 
same, hence the orbits of the planets are not true circles, but a 
little elliptical, and they must pass over unequal parts of their orbits, 
in equal portions of time. The cause of this inequality, in the 
sun's attractive influence^ is owing to its being exerted on a planet 
when at different distances from that luminary, and to its acting in 
different angular directions. 

It has been clearly demonstrated by Kepler and others, that, in 
passing round a point towards which it is attr^acted, a body passes 
over equal areas, in equal times. The whola of the space supposed 
to be contained within the earth's orbit, as represented in figure 1, 
of Plate VI. is divided into twelve areas or spaces, all of which, 
though of very different forms, some long and narrow, others broad 
and short, but they severally contain an equal quantity of space. 
An imaginary line drawn from the centre of the earth to that of the 
sun, and keeping pace with the earth in its revolution, passes over 
equal areas in equal times ; and consequently, as will be seen from 
the figure, will pass through unequal portions of its orbit in equal 

1. How is the force of gravitation m the sun counteracted ?— — 2. By what 

are the planets kept in their places? 3. Do the planets pass through equal 

portions of their orbits in equal times? 4. Why do they not? 5. Are 

the orbits of the planets true circles? G. Why are they not? 7. To 

what is owin;;- the inequality of the sun's attractive force on the planets ? 

— : — 8. What has been demonstrated by Kepler? 9. By which figure is 

this illustrated ? 10. How is that figure described ? 11. How is it seen 

by the figure that a planet passes through unequal pf)rtions of its orbit in 
equal times ? 



Flo 2^ 



PLATEVX, 



iH ^ Fi:_93 




Tia4 



^ f ^ 



^^''Ci 5 0f>^^ 



^ 7 



^jy V j^ ^^^ "^-^ 




^onj^ctio^ 



^t\^- 



^,'''' 



,V''' 




SitntincT in 
t/ie A'orthrrn 
Keiilisphfre 



^G~ 



^7^8 



-~~-~M 



B 






Summer in 
the Southern 
B^'mi.sjjlicrc' 




.'•'i)'"" 



ii^ 







''^ 






FIRST BOOK IN ASTRONOMY. 55 

times. Thus, while the space numbered 6, contains the same area 
as that numbered 12, the former contains only about one half as 
Kiuch extent of orbit as the latter. 

The reason for this inequality in the earth's velocity, as it moves 
in its orbit, may be explained in the following manner. Tn figure 
2, of Plate VI. let S represent the sun, A, the earth, and A E, the 
orbit of the earth. It will be seen that the sun is not in the centre 
of the orbit, but in one of the foci. Supposing the earth, when put 
in motion at A, had not sufficient projectile force to carry it round 
the sun in a circle, according to the direction C, it would, by the 
force of the sun's attraction, be drawn in an elliptical form, as de- 
noted by the letters B, K, and E. By this means, the attractive 
and projectile forces cease to operate in a right angular direction; 
the former acting much in the direction of the latter, till the earth, 
by the time of reaching its perihelion, has acquired about double 
the velocity it had in its aphelion. Likewise, in continuing its 
course from E, the velocity has become so great as to prevent it 
from revolving round the sun, in a small circle of the distance of E 
from S, that it recedes off in the direction G ; at which time its 
projectile force is so far abated as to be carried by the force of grav- 
ity from G to A, instead of being carried to H. As the earth's ve- 
locity was continually increasing in passing from A to E, in conse- 
quence of the two forces acting upon each other in an angular di- 
rection of less than ninety degrees, so in passing from A to E, the 
velocity was continually decreasing, in consequence of their acting 
upon each other in an angular direction of more than ninety 
degrees. 

The eccentricity of the earth's orbit is one million and a half 
miles ; making its perihelion distance about three millions of miles 
less than its aphelion distance from its centre of motion. Mer- 
cury's orbit, having an eccentricity of 7,500,000 of miles, will have 
its perihelion 15,000,000 of miles nearer to the sun than its aphelion. 



12. By which figure is the inequality of the earth's velocity in its orbit 

explained ? 13. In that figure, why is not the earth carried to the letter C, 

instead of being brought to B ? 14. Why in reaching its perihelion at E, 

does the earth acquire an increased velocity .'' 15. When at E, why does 

it not revolve in a small circle, instead of receding off to G.^ 16. When 

it reaches G, why does it not proceed on in the direction H, instead of being 

turned to A ? 17. What is the angular direction of the earth in passing 

from A to E ? 18. What is it in passing from E to A ? 19. Does the 

greater or lesser angular direction in circular motion tend to an increased ve- 
locity .' 20. What is the eccentricity of the earth's orbit.'' 21. Of Mer- 
cury's orbit? 



56 FIRST BOOK IN ASTRONOMY. 

The eccentricity of the orbit of Venus, being only half a million of 
miles, its perihelion varies but one million of miles from its 
aphelion. 

The orbits of the comets being very elliptical, the irregularity of 
their motions must be exceedingly great. When near the sun, or 
their perihelion, the centripetal force must act powerfully on the 
comet, and that force must be equalled by the projectile force, hence 
they will then raove with amazing celerity ; but when arrived at 
their aphelion, where the influence of the sun is weak, their motion 
is exceedingly slow, and the sun must appear little more than a 
fixed star. 



THE CENTRE OF GRAVITY. 
LESSON XXVII. 

The centre of gravity is that part of a body around which all its 
parts are so equally balanced, that if the body be suspended or sup- 
ported by the centre of gravity, it will rest in any position. Take 
a book, and find, by trial, under what part the finger must be placed 
to keep the book from falling; that point is the centre of gravity to 
the book. Take a rod, and find that place about the middle of it, 
under which the finger being placed it will be balanced ; that is 
the centre of gravity to the rod. 

The centre of gravity always descends first. The cork of a 
shuttlecock always comes down before the feathers. Tie a weight 
of any sort to the end of a stick, and toss it into the air, that end vyill 
always come down first. It is for this reason that the point of an 
arrow is made heavier than the other end. The most ignorant 
savages soon find from experience that they must make the point of 
their darts heavier than the other end, that the point may always be 
straight forward when thrown at a wild beast or at an enemy. 



22. What is the eccentricity of the orbit of Venus? 23. What is the 

difference between the perihelion and aphelion from the centre of motion, in 
each of these planets? 24. Why is the irregularity of the motion of com- 
ets so great? 25. Why is the motion of comets so great, when in their 

perihelion ? 2C. How is their motion in the aphelion part of their orbits ?. 

1. What is the centre of gravity ? 2. How may the centre of gravity of 

a book be found ? 3. In a rod how may it be found ? 4. Which part of 

a body always descends first? 5. What are instances of this? 6. Why 

is the point of an arrow made heavier than the other end? 



rmst BOOK IN ASTRONOMY. 5t 

If there were two balls of equal size fastened to the two ends of 
a rod, the whole might be considered as one body, and their com- 
mon centre of gravity would be the point equidistant from the two 
extremes. If one of the balls were greater than the other, the centre 
of gravity would be proportionally removed towards the larger one, 
till upon an ascertained point they would balance each other. Thus 
any two bodies suspended upon a point representing the commori 
centre of gravity, may balance each other. These bodies may be 
connected together by an imaginary as well as by a real rod or line j 
and upon the same principle, instead of two bodies thus united, the 
number may be increased to three, ten, or an hundred, and all be 
considered but one, suspended or balanced, upon the point, which 
is their common centre of gravity. 

Precisely in this way the planets of the solar system, including also 
the sun, have a common centre of gravity and balance each other. 
If there were but one body in the universe, provided it were of 
uniform density, the centre of it would be the centre of gravity, 
towards which all the surrounding portions would uniformly tend, 
and would thereby balance each other. Thus the centre of gravity, 
and consequently the whole body, would remain without any change 
of position. 

Accordingly, if we suppose the sun to be this body, it would for- 
ever continue without change of place. Why should it move? 
Where could it move 1 If the portion of matter on one side of 
this immense globe were to incline it in one direction, the portion 
of matter on the other side would equally incline it in a contrary 
way. Consequently it would not move at all. It cannot be said 
or supposed that the sun, according to the usual mode of speaking, 
would fall down. On the supposition made, up and down would be 
relative terms. On which ever side of this vast spheroid or globe, 
the supposition were to be applied, down would mean towards the 



7. If two balls of equal size be fastened to the two ends of a rod, where 

will be their common centre of gravity ? 8. How would the centre of 

gravity be situated if one ball were larger than the other ? 9. May bodies 

balance each other, when connected by an imaginary as well as by a real 

line ? 10. What is said of having a greater number of bodies than two 

thus balance each other? 11. What is there in nature precisely like this? 

1*2. Where would be the centre of gravity in a body, provided there 

were no other body in existence ? 13. Under what circumstances might 

a body remain v/ithout any change of position ? 14. What is the course 

of reasoning when supposing the sun to be the only body in existence? 

15. What is said of the terms up and down ? 16. What might the terna 

down in the supposition made be understood to mean ? 

H 



58 FIRST BOOK IN ASTRONOMY. 

centre of it. And as the sun and all the planets of the solar sys* 
tern may be viewed as one body, connected by imaginary lines, 
with a common centre of gravity, they of course balance each other, 
and forever will continue in the position they now occupy, unless 
moved therefrom by some other body or bodies existing in the re- 
gions of space. 

If the earth were the only attendant on the sun, as its quantity 
of matter is computed to be 330,000 times as great as that of the 
earth, it would revolve in a circle a 330,000th part of the earth's 
distance, in the same time as the earth is making a revolution in 
its orbit, or in one year ; but as the planets in their orbits must vary 
in their positions, the centre of gravity cannot always be at the 
same distance from the centre of the sun. 

The quantity of matter in the sun so far exceeds that of all the 
planets together, that even if they were all on the same side of it,, 
astronomers assert that this luminary would never be more than its 
own diameter from its own centre of gravity. And since the suri 
is so little attracted from its own place, by the influence of the sur- 
rounding bodies in the system, it is very properly considered the 
centre of the system, ^ 



• PERIODICAL CHANGE OF SEASONS. 
LESSON XXVIII. 

The variety of the seasons depends upon the length of the days 
and nights, and upon the position of the earth with respect to the 
sun. The orbit in which the earth revolves in its annual course 
round the sun is not, as stated in a previous lesson, a circle, 
but an ellipse or oval ; and we are more than three millions of miles 
nearer to the sun in December, about the winter solstice, than we 
are in June about the time of the summer solstice. 

Now as heat and light from the sun are greater as the distance is 
less, it is manifest that this circumstance would occasion a variation 

17. How is it said the sun and planets may be viewed in relation to this 
subject ? 18. What supposition is made of the earth's being the only at- 
tendant on the sun ? 19. Why is the common centre of gravity to the solar 

system continually varying ?— ^ — 20. How much might it vary if all the 

planets were to be on the same side of the sun ? 21. Why is the sun 

considered the centre of the system ? 

1. On what depends the variety of the seasons? 2. What is said of the 

orbit of the earth.? 3. When are we nearest to the sun? 4. And how 

much ? 



FIRST BOOK IN ASTRONOMY. 59 

in the temperature of the air, like that of oar seasons, if the equator 
always coincided with the ecliptic. But the seasons with us, in 
north latitude, are not in the least degree occasioned by this cir- 
cumstance, but by the direction in which the sun's rays fall upon 
us. When they fall perpendicularly, or nearly so, the season is 
warmest ; and when they fall most obliquely, or in a slanting man- 
ner, the season is coldest. The cause of the difference in the 
obliquity of the sun's rays, is the obliquity of the ecliptic, or the in- 
clination of the earth's axis. 

The axis of the earth inclines or leans to the plane of the eclip- 
tic 231 degrees. Figure 8, of Plate VI. represents the sun and the 
earth in four different parts of its orbit. When the earth is at 
B and D, the sun shines from pole to pole, causing days and nights 
of equal length, on the 20ch of March, and the 23d of September. 
When at A, it represents the earth with the north pole turned 
away or inclined from the sun, as on the 23d of December. And 
when at C, it represents the north pole inclined towards the sun, as 
on the 21st of June. From figure 7^ of Plate VIII. it will also be 
seen that a much smaller portion of winter than of summer rays 
will fall upon a given surface in consequence of the different degrees 
of obliquity with which they reach it. 

The effect of obliquity in regard to the sun's rays, will be further 
evident from a very simple experiment. Let a piece of board be 
held perpendicularly before the fire. It will then receive a body of 
rays equal to its breadth. But if it be placed obliquely, at an angle 
of forty-five degrees, then only half the rays will fall on its surface, 
and the other half wall pass over it ; so it is with the surface of the 
earth in summer and winter. 

The circumstance, also, that the days are longest, whether in 
north or south latitude, when the sun's rays fall in the greatest 
quantity and most directly at any place, contributes much to the 
warmth of summer and to the cold of winter. In northern coun- 
tries, where the days are eighteen or twenty hours long, or where 
the sun is above the horizon for any number of days together, the 
heat of summer is equal to that of any part of the world. 

.5. Are our seasons occasioned by this ? — —3. By what are they occasioned ? 

7. On what depends the obliquity of the sun's rays ? 8. How much 

is the axis of the earth inclined ? 9. What does figure 8, of Plate VI, rep-" 

resent' 10. How does the sun shine on the earth when at B and D ? . 

11. What season is represented when at A? 12. And when at C, what 

one is represented? 13. What is explained by figure 7, of Plate VIII ? .' 

14. How is this illustrated by a piece of board ? 15. How does the length 

of the days and nights affect the seasons ? 1(3. What is said of countries 

where the sun is for several days together above the horizon ? 



60 FIRST BOOK IN ASTRONOMY. 

Since the degree of heat from the sun increases as the earth's 
distance diminishes, and this distance is least when it is summer in 
south latitude, and greatest when it is summer in north latitude, a 
greater degree of heat, thereforej must be received in summer in 
south latitude, than in summer in north latitude. But to compen- 
sate for a less degree of heat, the inhabitants in north latitude 
have longer summers than those in south latitude. For as the sun 
is Rot in the centre of an ellipse but in one focus, the earth must 
move farther jn its orbit in one part of its revolution than in the 
other. It moves slower also as it is farther from the sun ; and our 
summers are found to be eight days longer than the summers in 
pouth latitude ; that is, between the vernal and autumnal equinoxes 
there are eight days more than between the autumnal and vernal. 

It is well known that the degree of heat is not greatest when the 
days are longest, We have the warmest weather in the latter part 
pf July, and in the first of August ; and our coldest month is Jan- 
uary. To account for this it has been stated, that a body once 
heated does not grow cold again instantaneously, but gradually; 
now as long as more heat comes from the sun in the day than is 
|o$t in the night, the heat of the e^rth and the air will be daily in?- 
creasing, and this must evidently be the case for some weeks after 
the longest day, both on account of the number of rays which fall on 
3, given space, and also from the perpendicular direction of those 
rays. It is for the same reason, that the warmest part of the 
day is not, when the sun is at Ihe meridian, but ajjout two or thre§ 
p'clock in the afternoon. 



SUCCESSION OF DAY AND NIGPIT. 

LESSON XXIX. 

By the daily motion of the earth on its axis, the same pheriom* 
ena appear as if all the celestial bodies turned round it ; so that in 
its rotation from west to east, when the sun or a star just appears 
above the horizon, it is said to be rising, and as the earth continues 
its revolution, it seems gradually to ascend till it has reached its 

17. In what proportion does the heat of the sun increase ? 18. Why is 

a greater degree of heat from the sun received in southern than in northern 
latitudes .'' 19. How is this less degree of heat in northern latitudes com- 
pensated ? 20. Why does the earth move faster in one part of its orbit 

than in another part i' 21. How much longer are the summers in northern 

than in southern latitudes ? 22. At what times in the year is our degree 

of heat the greatest ? And greatest degree of cold ? 23. Why is this ? 

24. Why is it warmer about two o'clock in the afternoon than when the sun 
^3 at meridian height ? 

1. What phenomena are exhibited from the daily motion of the eeirth ? 



FIRST BOOK IN ASTRONOMY. 61 

meridian; here the object has its greatest elevation, and begins to 
decline till it set, or become invisible on the western side. In the 
same manner the sun appears to rise and run its course to the 
western horizon, where it disappears, and night ensues, till it again 
illuminate the same part of the earth in another diurnal revolution. 

One half of the earth's surface is constantly illuminated, and by 
its regular diurnal motion, every place is successively brought into 
light and immersed in darkness. If the axis of the earth were al- 
ways perpendicular to the plane of the ecliptic, the dajs would 
everywhere be of the same length, and just as long as the nights. 
For an inhabitant at the equator, and one on the same meridian to- 
wards the poles, would come into the light at the same time, and on 
the other side would immerge into darkness at the same time. And 
since the motion of the earth is uniform, they would remain in the 
ddrk hemisphere just as long as in the light ; that is, their day and 
night would be equal — the plane of the ecliptic coinciding with 
the plane of the equator. 

But as the ecliptic and equator make an angle with each other 
of twenty-three and a half degrees, or in other words, as the axis of 
the earth has such an inclination to the plane of its orbit, it is mani- 
fest that, except the earth be in that part of its orbit where the eclip- 
tic cuts the equator, an inhabitant at the equator and one on the 
same meridian towards the poles, will not come into the light at the 
same time, nor, on the other side, immerge into darkness, at the 
same time. And since the axis of the earth always preserves the 
same inclination, they will, except at the points where the two 
great circles intersect each other, remain in the dark and light 
hemispheres at different times ; that is, their day and night will be 
unequal. 

The points where the equator cuts the ecliptic are the begin- 
ning of the signs Libra and Aries. The earth is at these points of 
its orbit, or, as is commonly said, the sun enters the sign Aries on 
the twentieth of March, and the sign Libra on the twenty-third of 
September. Hence at these periods, and at no others, the days 
and nights are equal all over the world ; and on this account they 

2. How much of the earth's surface is constantly illuminated ? 3. Is 

the same portion always illuminated ? 4. How does it vary ? 5. Under 

what circumstances would the days and nights everywhere be of the same 

length? 6. How is this explained? 7. How would then be situated 

the plane of the ecliptic in regard to the plane of the equator ? S. Why is 

not the day and night always equal to an inhabitant at the equator, and to one 

on the same meridian towards the poles ? 9. How is this explained ? 

10. Since the axis of the earth is thus inclined, at what seasons will the 

days and nights be equal? 11. At what points does the ecliptic cut the 

equator ? 



63 FIRST BOOK IN ASTRONOMY. 

are called equinoxes ; the first, the vernal, and the second, the 
autumnal equinox. 

At these seasons the sun rises exactly in the east at six o'clock, 
and sets exactly in the west at six o'clock ; the light of the sun is then 
terminated by the north and south poles, and as all parts of the earth 
turn round once in twenty four hours, every place must receive 
the rays twelve hours, and be deprived of them for the same time. 
But at other seasons, where the rays of light are not terminated by 
the north and south poles, but extend over the one and do not reach 
the other, it must be manifest, from a moment's inspection of the cir- 
cles drawn on globes, or common maps of the world, that day and 
night will be unequal in all places except those situated on the equa- 
tor, where they will always be equal. 

At the poles there is but one day and one night in a year, each 
of six months. The sun can never shine beyond a pole farther 
than twenty-three and a half degrees ; for that is the extent of the 
declination ; and when it has declination from the celestial equator 
either north or south, it must shine beyond one pole, and not to the 
other. The days, therefore, will be longest in one hemisphere 
when they are shortest in the other. 

The subject of this lesson may be illustrated by hanging a small 
terrestrial globe or any other round body above or below the level 
of a candle, so as to correspond with the sun's declination. It will 
be seen, that the light shines over one pole, and does not reach the 
other. If the globe or ball be then turned, it will be observed, that 
the circles performed by any parts of the surface are unequally di- 
vided by the light ; that it will be constant day or night near the north 
pole, as the ball is depressed or elevated, and that all the phenom- 
ena will be reversed in the other, or lower hemisphere. 

The inhabitants of the polar regions are not in total darkness, 
even when the sun is absent. Twilight continues to enlighten 
them a great portion of the time. Besides this the moon is above 
the horizon of the poles, a fortnight together. And further to as- 
sist in mitigating the darkness, their full moons have the highest 
altitude, describing nearly the same track as their summer sun. 

12. Why are these points called equinoxes ? 13. How are they distinguish- 
ed from each other t 14. At what hour and where does the sun rise at this 

season 1 15. At what hour and where does it set .? IG. How long is day 

and night at the poles .^ 17. How far beyond the poles of the earth may 

the sun shine t 18. Why not more ? 19. How do the lengths of the 

days and nights in different hemispheres correspond 'i 20. How may the 

subject of this lesson be illustrated.? 21. Does the ab.sence of the sun 

in polar regions cause the inhabitants to be in total darkness .'' 22. By what 

means is this prevented .'' 



FIRST BOOK IN ASTRONOMY. 63 

FORMS AND DIVISIONS OF TIME. 
LESSON XXX. 

Time, as measured by the heavenly bodies, is divided intoyear^^ 
months, weeks, days, hours, minutes, and seconds. Years are of 
tvv^o kinds, tropical and sidereal. A tropical year, which is alsa 
called the natural year, is the period which the earth takes in pass- 
ing through the signs of the zodiac, and consists of 365 days, 
5 hours, 48 minutes, and 51 2 seconds. A sidereal year is the 
time that the sun apparently occupies in passing from a fixed star to 
its arrival at the same star again ; and is 365 days, 6 hours, 9 min- 
utes, and 12 seconds. 

What is called the common or civil year, is usually reckoned at 
365 days ; and hence, as the tropical year consists of about 365^ 
days, every fourth civil year must contain 366 days. The civil 
year is divided into twelve months ; of which one has 28 days, sev- 
en have 31 days each, and four have 30 days each. Every fourth 
year the month of February has 29 instead of 28 days. 

As the form of the year is various among different nations, so is 
its beginning. The Jews, like many other nations of the East, had 
a civil year, which commenced with the new moon in September ; 
and an ecclesiastical year, which commenced from the new moon 
in March. The Jewish year consisted of 354 days, or twelve lunar 
months ; and to every third year a month was added, so as to make 
the lunar and solar year coincide. 

The Persians begin their year in the month answering to our 
June: the Chinese, and most of the inhabitants of India, begin it 
with the first new moon in March ; and the Greeks with the new 
moon that follows the longest day. In England and America, the 
legal or civil year formerly commenced on the 25th of March, and 
the historical year on the first of January. But since the alteration 
of style, which took place in 1752, the civil year in both countries 
has likewise begun on the first of January. 



1. How is time divided, when measured by the heavenly bodies ?— — 

2. What is a tropical year ? 3. What is a sidereal year ? 4. How long 

is the civil year ? 5. What comparison is made between the civil and trop- 
ical year ? 6. How is the civil year divided ? 7. What are the lengths 

of the different months ? 8. What is the difference between the civil and 

ecclesiastical year of the Jews? 9. How long was their year? 

10. When do the Persians begin their year ? 11. When do the Chinese ? 

12. When do the Greeks ?- 13. How does the year begin in England 

and America ? 



64 FIRST BOOK IN ASTRONONY. 

Months are astronomical and civil. An astronomical months 
■svhich is also called the natural month, is measured by the motion 
of the earth or moon. If measured by the former, it is called the 
solar month. If measured by the latter, it is called the lunar month^ 
A lunar month is the time the moon takes to revolve round the 
earth, being 27 days, 7 hours, and 43 minutes. A solar month is 
that period of time occupied in passing through one of the signs of 
the zodiac, and is found to contain 30 days, 10 hours, and 29 min- 
utes. The length of time in a solar month, is ascertained by di- 
viding the solar year into twelve equal portions. 

Civil m.onths are those which are established to answer the pur- 
poses of life, and do not greatly vary in length of time from astro- 
nomical months, whether solar or lunar. January received its name 
from Janus, a Roman deity ; February, from Februa, a festival held 
in this month, by the Romans; March, from Mars, the god of war ; 
April, from the Latin word aprilis or aperio, which means to open, 
the leaves and blossoms opening this month; May, from the Latin 
word Mains ; June, from the Latin word Junius, or the goddess 
Juno; July, from Julius, the surname of Caesar, the Roman Dicta- 
tor ; August, from Augustus Cssar ; September, from a Latin 
word, which means' seven, it being the seventh month from March ; 
October, from a Latin word, which means eight, it being the eighth 
month from March; November, from a Latin word, which means 
nine, it being the ninth month from March ; and December, from 
a Latin word, which means ten, it being the tenth month from 
March. 

Till the time of Augustus Cssar, the sixth month was called 
Sextilis. In honor of that emperor, as already stated, it was chang- 
ed to August. And, to increase the honor intended him, a day 
was taken from the last of February, and added to August. Pre- 
viously to this time August consisted of but thirty days, and Feb- 
ruary, in a common year, had twenty-nine. 



14. What is the difference between a lunar and a solar month ? 15. How 

long is the lunar month ? 16. How long is the solar month.' 17. How 

is the length of the solar month ascertained .' IS. What are civil months ? 

19. From what did January receive its name ? 20. From what did 

February ? 21. From what did March.' 22. From what did April : 

23. From what did May ? 24. From what did June ? 25. From what 

did July .' 26. From what did August .' 27. From what did Septem- 
ber .^ 28. From what did October.' 29. From what did November .^ 

30. From what did December .' 31. "What other honor was rendered 

the emperor Augustus CfBsar besides calling one of the months after his 
name ? 



FIRST BOOK IN ASTRONOMY. 65 

The days of the week received their names in the following 
manner. The first day of the week was called Sunday, from the 
Sun, to which by the ancient heathens it was dedicated ; Monday, 
from the Moon ; Tuesday, from the Saxon word, Tuisco, and is 
the same as Mars ; Wednesday, from a Saxon word, Woden, a hea- 
then deity ; Thursday, from the Saxon word, Tlior ; Friday, from 
Friga, a Saxon goddess ; and Saturday, from two Saxon words, 
which signify the day of Saturn. Christians call the first day of 
the week Sunday, in honor of Jesus Christ the Saviour of the 
world, who is denominated the Sun of Righteousness. 

The ancient Athenians and Jews began their day at sunsetting, 
which custom is followed by the modern Austrians, Bohemians, Si- 
lesians, Italians, and Chinese. The ancient Babylonians, Persians, 
Syrians, and most of the eastern nations, began their day at sunrise. 
The Egyptians and Romans began their day at midnight, and are 
followed by the English, the Americans, French, Germans, Dutch, 
and Portuguese. The Arabians begin their day at noon. 



ON THE EQUATION OF TIME. 

LESSON XXXI. 

The natural or solar day is the time which the sun takes in pass* 
ing from the meridian of any place till it comes round to the same 
meridian again ; or it is the time from noon to noon. A sidereal 
day is the time in which the earth revolves once about its axis, as 
determined by the fixed stars. The rotation of the earth is the 
most equable and uniform motion in nature, and is completed in 
twenty-three hours, fifty-six minutes, and four seconds; for any me- 
ridian on the earth will revolve from a fixed star to that star again 
in this time. Sidereal days, therefore, are all of the same length; 
but solar or natural days are not. The mean length of a solar day 
is twenty-four hours, but is sometimes a little more, and sometimes 
a little less. 

32. How did the days of the week receive their names .^ 33. Why do 

Christians call the first day of the week Sunday ? 34. What nations be- 
gin their day at sunsetting? 35. What ones at sunrise ? 36. What ones 

at midnight .' 37. By whom is the day begun at noon ? 

1. What is a natural or a solar day .'' 2. What is a sidereal day.' 

3. What is said of the rotation of the earth ."* 4. What is the mean length 

of solar days ? 



66 FIRST BOOK IN ASTRONOMY. 

The reason of the difference between the solar and sidereal day 
is, that as the earth advances almost a degree eastward in its orbit, 
in the same time that it turns eastward round its axis, it must make 
more than a complete rotation before it can come into the same 
position with the sun that it had the day before ; in the same way, 
as when both the hands of a watch or clock set off together, as at 
twelve o'clock, for instance, the minute hand must travel more than 
a whole ciicle before it will overtake the hour hand, that is, before 
they will be in the same relative position again. It is on this ac- 
count that the sidereal days are found to be on an average, shorter 
than the solar ones by three minutes and fifty-six seconds. 

As a clock is intended to measure exactly twenty-four hours, it is ev- 
ident that, when a solar day consists of more than twenty-four hours, 
it will not be noon by the sun till it is past noon by the clock ; in 
which case the sun is said to be slow of the clock. But when a 
solar day consists of less than twenty-four hours, it will be noon by 
the sun before it is noon by the clock ; and the sun is then said 
lo be fast of the clock. 

The time measured by a clock is called equal or mean time, and 
that measured by the apparent motion of the sun in the heavens 
or by a sundial, is called apparent time. The adjustment of the 
difference of time, as show^n by a well regulated clock and a true 
sundial, is called the equation of time. 

There are two reasons for the difference between the sun and a 
well regulated clock. One of these reasons is the inclination of 
the earth's axis to the plane of its orbit. The other is the inequality 
of the earth's motion in its orbit. This orbit is an ellipse, and the 
motion of the earth is quicker in its perihelion than in its aphelion. 
This inequality in the earth's motion causes our summer half year 
to be about eight days longer than the winter half year; 

There are in the course of the year, as many mean solar days as 
there are true ones, the clock being as much faster than the sun- 
dial on some days of the year, as the sundial is faster than the 



5. What is the reason for the difference between the solar and sidereal 
days ? 6. How is this illustrated hy the hands of a watch ? 7. How- 
much shorter are sidereal days than solar days, on an average P 8. How is 

a clock intended to measure time ? 9. When is the sun said to be slow of 

the clock ? 10. And when fast of the clock ? 11. What is called mean 

time.'' 12. What is called apparent time ? 13. What is the equation of 

time.' 14. What are the reasons for the difference between the sun and 

a well regulated clock .' 15. How much longer is the summer half than 

the winter half of the orbit ? 16. How does the number of mean solar 

days compare as to number with true ones.'' 



FIRST BOOK IN ASTRONOMY.- 67 

clock on others. Thus the clock is faster than the sundial from 
the 24th of December to the 15th of April, and from the 16th 
ofJune, tothe 31stof August; but, from the 15th of April to the 16th 
of June, and from the 31 st of August to the 24th of December, the sun- 
dial is faster than the clock. On ti^e 15th of April, the I6th of June, 
the 31st of August, and the 24th of August, the clock and sundial 
perfectly coincide, and the true solar day is exactly twenty-four hours. 
Since the stars are found to gain three minutes and fifty-six 
seconds upon the sun every day, amounting in a year to one di- 
urnal revolution, it follows that, in three hundred and sixt3'-five 
days, as measured by the sun, there are three hundred and sixty- 
six days as measured by the stars. This regular return of the fixed 
stars to the meridian affords an easy method of determining wheth- 
er our clocks and watches keep true time. Make the trial in the fol- 
lowing manner. Let a small hole be made through the window 
shutter; or in a thin plate of metal fixed for that purpose. Then 
observe at what time in the night a particular star disappears be- 
hind a chimney or some other object at a small distance. Do the 
same on the next night ; and if it disappears, on the second night 
three minutes and fifty-six seconds sooner by the clock or watch than 
it did the night previous ; do the same night after night, and if you 
continue to observe the same variation in the stars disappearing, 
it is certain that the timepiece goes right. But, if this result 
does not take place, it is certain that the timepiece is not accurate. 



LEAP YEAR AND NEW STYLE. 

LESSON XXXII. 

In Lesson XXX, there has been given an account of the divisions 
of time. Julius Caesar, finding that the lunar year was ten days 
shorter than the solar year, was induced to reform the calendar ; 
and did accordingly introduce the system of computation which 
has borne his name to the present time. In this mode of reckon- 
ing time, the Julian year, as our year is called, consists of 365,, 



17. Whon is the clock faster than the sundial ? 18. When is it slower 

than the sundial ? 19. When do they perfectly coincide ? 20. How 

does it appear that in a year measured by the stars, there is one day more than 

in a year measured by the sun ? 21. How may the accuracy of clocks be 

determined ? 

1. From whom does the Julian year take its name .' ■2. Of what doea 

this year consist .-' 



68 FIRST BOOK IN ASTRONOMY. 

days, and six hours. To allow for the six odd hours, every fourth 
year, a day was to be added to the month of February, the 24th of 
that month being reckoned twice. This year was thus made to 
consist of 366 days, and is called leap year. 

The 24th of February being what the Romans called sex^o calen- 
das Martii, that is, the sixth of the calends of March, the addi- 
tional or intercalary day was called bis sexto calendas Martiiy that 
is, the second sixth of the calends of March, and hence in our 
almanacs leap year is denominated Bissextile, Instead of repeat^ 
ing the 24th of February, we place the additional day at the end 
of the month, which becomes the 29th day. 

To ascertain the time when leap year or bissextile will return, 
divide the date of the year by four, and if there is no remainder, it 
is leap year. Thus, 1820, 1824, 1828, and 1832 are leap years, 
because when divided by four there is no remainder. When the 
year is divided by four, if one is the remainder, it is the first year 
after leap year, or bissextile ; if the remainder is two, it is the sec- 
ond after; if the remainder is three, it is the third after. Hence 
1829 would be the first year after leap year ; 1830, the second 
after ; and 1831, the third after. 

The Julian year, consisting of 365 days and six hours, and the 
true solar year, as stated in a previous lesson, being a few minutes 
short of this, the difference amounts in a little less than 130 years, 
to a whole day. This difference at the time of Pope Gregory, who, 
in 1582, undertook further to improve the calendar, amounted to 
ten days. Accordingly, it was ordered that the 5th of October 
should be called the 15th. The style thus altered was called the 
Gregorian or new style. Though adopted and used in several 
countries of Europe, it was not received in England till the year 
1752. The old style or Julian calendar still prevails in Russia. 
The difference between the old style and the new, in the present 
century, is twelve days. 



3. How did he provide for the six odd hours ? -4. What is the year of 

366 days called ? 5. By what name is it called besides leap year ? 

6. Why is it called bissextile ? 7. How is leap year determined ? 

8. What illustrations are given ? 9. If the year divided by four has a re- 
mainder, what does that denote ? -10. What are the three illustrations ? 

11. Is there any difference between the Julian year and the true solar year? 
12. To what will this difference amount in 130 years ? 13. Who fur- 
ther improved the calendar? 14. When? 15. How did he doit? 

16. What is the improvement called ? 17. When was new style received 

in England ? 18. What country still retains the old style ? 19. What 

jp the present difference between new and old style ? 



FIRST BOOK IN ASTRONOMY. 69 

In order to prevent a similar future discrepancy between the 
tropical and civil year, it was ordered, on the adoption of the Gre- 
gorian or new style, that bissextile shall be omitted three times in 
every four hundred years. When the centuries of the Christian 
era are divided by four, if nothing remain, the leap year is to be 
retained. But if there be a remainder, the year is to be reckoned 
common. Accordingly the closing year of every fourth century is 
bissextile. Thus 1600 and 2000 are leap years ; but 1700, ISOO, 
and 1900 are common years of 365 days. With this mode of 
computation it will require a period of nearly 5000 years in order 
to produce a difference of a single day between the civil and trop- 
ical year. 



ON THE REFRACTION OF LIGHT. 
LESSON XXXIII. 

Whatever suffers the rays of light to pass through it, is called 
a medium, and the more transparent the body, the more perfect is 
the medium. But the rays of light do not pass through a transpa- 
rent medium, unless they fall perpendicularly upon it, in precisely 
the same direction in which they were moving before they entered 
it. They are bent out of their former course, and this is called re- 
fraction. 

When the rays of light pass out of a rarer into a denser medium, 
as from air into water or glass, they are always refracted towards a 
perpendicular to the surface, and the refraction is more or less, in 
proportion as the rays fall more or less obliquely on the refracting 
surface. In figure 3, of Plate VIII, the ray B C in passing into a 
denser medium is refracted to F, towards the perpendicular A E, 
instead of proceeding forward in a right line to D. But when the 
rays pass from a denser to a rarer, as from glass or water into air, 
they move in a direction further from the perpendicular. This is 



20. What method was adopted to prevent a similar discrepancy between 

the tropical and civil year? 21. What illustrations are given .' 22. With 

the present improved Gregorian method of computation, how long a period 
will be necessary to make the difference of a day between the civil and the 
tropical year .' 

1. What is a medium .' 2. On what does its quality depend .' 3. What 

takes place M-hen rays of light pass from a rarer to a denser medium .' 

4. In what proportion will they be refracted .? 5. How is figure 3, of Plate 

VIII, to be explained .' G. What takes place when rays of light pass from 

a denser to a rarer medium r 



70 FIRST BOOK IN ASTRONOMY. 

represented in figure 2, of Plate VIII. The ray B C, if it pro- 
ceeded forward in a right line, would reach the letter F ; but by 
passing into a rarer medium, it is refracted from the perpendicular 
A E, to the point D. 

If a piece of money is placed in an empty basin, and the spec- 
tator is stationed so far distant as not to be able to see it, no sooner 
is the basin filled with water, than the money will be distinctly seen. 
Here the rays of light pass from the air, a rarer, into water, a denser 
medium, and are refracted from the perpendicular, and thus meet 
the eye. This is illustrated in figure 6, of Plate VIll. The eye 
of the spectator is at A, the money is placed in the empty basin at 
C, and cannot be seen ; but when filled with water it is seen at B. 

It is an established maxim in optics, that we see everything in 
the direction of that line in which the rays approach us last. If 
you place a candle before a looking glass, and stand before it, the 
image of the candle appears behind it ; but, if another looking 
glass be so placed as to receive the reflected rays of the candle, 
and you stand before this second glass, the candle will appear be- 
hind that ; because the mind imagines every object to be in the 
direction from which the rays come to the eye last. 

Rays of light, coming from a heavenly body, unless it be in the 
zenith, will be refracted or bent downward, in passing through our 
atmosphere. As the atmosphere is more and more dense, the 
nearer to the surface of the earth, these rays will be continually 
yielding to additional refraction. Thus the atmosphere represents 
different media, as A, B, C, and D, of figure 5, on Plate VI. On 
passing from one media to another, as b, c, d, and e, a new refrac- 
tion of the ray a b will take place ; but as the atmosphere is of an 
uniform variation in density, a ray of light passing through it, will 
proceed in a regular curve line, as m n, in that figure. 

In consequence of this refraction, heavenly bodies, when in the 
horizon, appear higher than they are. The effect of this refraction 
is about six minutes of time, but the higher they rise, the less they 
are refracted ; but when they are in the zenith, as already said, 



7. How is this explained by the figure? 8. What simple illustration is 

given of the refraction of light with a piece of money ? 9. By which fig- 
ure is this shown ?- 10. What established maxim in optics is named? 

11. How is this shown by the candle and the looking glass ? 12. What is 

said of rays of light coming from a heavenly body .'' 13. What does fig- 
ure 5, of Plate VI, represent? 14. How is the figure to be explained ? 

15. What amount of time is this refraction ? 



FIRST BOOK IN ASTRONOMY. 7l 

they suffer no refraction. The sun is visible on this account about 
three minutes before it rises, and about the same time after it sets ; 
making an increase of six minutes to the length of each day. In 
figure 4, of Plate VIII, E E represent a portion of the earth's sur- 
face, and the small dots denote the atmosphere. Although the sun 
is below the horizon, at S, yet a ray of light coming from the cen- 
tre of it, on reaching the atmosphere at A will be refracted to B, 
and will thereby cause the sun to appear in the horizon at C. 

In figure 8, of Plate VIII, the same phenomena are displayed. 
D E F represent the earth, and ABC the atmosphere. The sun 
being below the horizon at T, a ray of light T I, when falling on 
the atmosphere is turned out of its direct, or rectilineal course, 
and is so bent down to the eye of the observer at D, that the sun 
appears in the direction of the refracted ray at S, above the hori- 
zon, H D. On the same account, a star in the heavens at a, will 
appear at b to the eye of the spectator, D. 



TWILIGHT, OR CREPESCULUM. 
LESSON XXXIV. 



Twilight, also called crepesculum, is the time from the first dawn 
in the morning, to the rising of the sun ; and again, between the 
setting of this luminary and the last remains of day. By means of 
the atmosphere it happens that though none of the sun's direct rays 
can come to us after it is set, yet we still enjoy its reflected light 
for some time, and night approaches by degrees ; for after the sun 
is hidden from our eyes, the upper regions of our atmosphere re- 
main for some time exposed to the sun's rays, and from thence the 
whole is illuminated by reflection. 

It is usually computed that the twilight commences and termi- 
nates when the sun is about eighteen degrees below the horizon. 
Hence in high latitudes, during that part of the year in which the 
sun is never eighteen degrees below the horizon, there is continual 



16. What is said of the sun's being visible below the horizon ? 17. How 

is this explained by figure 4, of Plate VIlI ? 18. How is the satne shown 

by figure 8, of Plate Vlll ? 19. How is the difference between the real 

and apparent situation of a star shown by that figure ? 

1. By what other name is twilight called? 2. What is twilight ? 

3. How is it occasioned .? 4. At what time does it commence and termi- 
nate .? 5. What is said of twilight in high latitudes ? 



72 FIRST BOOK IN ASTRONOMY. 

twilight, from sunsetting to sunrising. This appears to be one of 
the beneficent allotments of the Deity, for mitigating the darkness 
of polar nights. 

As the twilight depends much on the quantity of matter in the 
atmosphere fit to reflect the sun's rays, the duration of it will be 
somewhat various. The height of the atmosphere, also, has an in- 
fluence in determining the period of its continuance. For instance, 
in winter, when the air is condensed with cold, and the atmosphere 
upon that account lower, the twilight will be shorter ; and in sum- 
mer, when the limits of the atmosphere are extended by the rarefac- 
tion and dilatation of the air of which it consists, the duration of the 
twilight will be greater. And for the like reason, the morning 
twilight, (the air being at that time condensed and contracted by 
the cold of the preceding night,) will be shorter than the evening 
twilight, when the air is more dilated and expanded. 

It is entirely owing to the reflection of the atmosphere, says Dr. 
Kiell, that the heavens appear bright in the day time. For without 
it, only that part of the heavens would be luminous in which the 
sun is placed ; and, if we could live without air, and should turn 
our backs to the sun, the whole heavens would appear as dark as in 
the night. In this case, also, we should have no twilight, but a 
sudden transition from the brightest sunshine to dark night, imme- 
diately upon the setting of the sun. 

In such a case as this-, even in the day time, during the shining 
of the sun, the least stars would be seen as plainly as in the darkest 
night, because there would be nothing to reflect the sun's rays to 
the eyes; and all the rays that do not fall upon the surface of the 
earth, passing by us, would either illuminate the planets and stars, 
or, spreading themselves out in infinite space, would never be re- 
flected back to us. But as the atmosphere surrounds the earth, 
which is strongly illuminated by the sun, it reflects the light back 
to us, and causes the whole firmament to shine with such splendor, 
as to obscure the faint light of the stars, and render them invisible. 



6. What is the advantage of it in high latitudes? 7. On what does twi- 
light much depend ? 8. Why is twilight short in winter ? 9. And more 

extended in summer ? 10. Why is the morning twilight longer than even- 
ing twilight? 11. How would the heavens appear, if it were not for the 

reflection of the atmosphere? 12. How would be the change from day to 

night, and from night to day ? 13. Under what circumstances might the 

stars be seen in the day time ? 14. Why are they not seen in the day 

time ? 



TZA^TE. VH. 




FIRST BOOK IN ASTRONOMY. 73 

Kepler supposed that twilight might be caused by the luminous 
matter about the sun. This may lengthen the time of its continu- 
ance, by illuminating the air, when the sun is too low to reach it 
with its own light ; but that the twilight is occasioned, as has been 
stated, by the refraction of the atmosphere, is too evident to admit 
a doubt. 



LUNAR AND SOLAR ECLIPSES. 
LESSON XXXV. 

The earth being a dark or opaque body enlightened by the sun, 
necessarily projects a shadow into the regions of space in a con- 
trary direction. When it so happens that the moon, in the course 
of its revolution about the earth, falls into the earth's shadow, it 
loses the sun's light, and appears to us eclipsed. As this happens 
when the earth passes between the sun and the moon, a lunar 
eclipse can of course take place only when the moon is full or in 
opposition. This may be illustrated by figure 2, of Plate VII. 

But the moon is not eclipsed every time it is full, or in opposition 
to the sun, because its orbit does not coincide with the plane of 
the earth's orbit, one half being about five degrees and a third above 
it, and the other half as much below it ; and therefore, unless the 
full moon happen in or near one of the nodes, that is, in or near 
the points in which the orbits intersect each other, it will pass above 
or below the earth's shadou', in which case there can be no eclipse. 
If the moon be within twelve degrees from the node at the time 
when it is full, there will be a partial or total eclipse, according as 
a part, or the whole of its disc falls into the shadow of the earth. 
See figure 4, of Plate VI. 

As the shadow of the earth is considerably wider than the diam- 
eter of the moon, an eclipse of the moon sometimes may continue 
for several hours. It is by knowing exactly at what distance the 
moon is from the earth, and of course the width of the earth's 

15. What did Kepler suppose might cause the twihght ? 

1. How is an eclipse of the moon occasioned ? 2. At what time can the 

moon be eclipsed ? 3. Which figure represents a lunar eclipse ? 4. How 

mav that fiorure be explained r 5. Why is not the moon eclipsed at every 

time of being full r 6. How near the node must the moon be in order to 

be eclipsed ? 7. By which figure is this illustrated ? 8. Why does an 

eclipse of the moon continue so long t 8. How is it that eclipses can be 

calculated with so much accuracy .' 
K 



74 FIRST BOOK IN ASTRONOMY. 

shadow at that distance, that eclipses are calculated with the great- 
est accuracy, many years before they happen. Lunar eclipses are 
visible over every part of the earth that has the moon at that time 
above the horizon; and the eclipse appears of the same magnitude 
to all, from the beginning to the end. 

An eclipse of the moon is partial, when only a part of its disc 
is w^ithin the shadow of the earth ; it is total, when all its disc is 
within the shadow ; and it is central, when the centre of the earth's 
shadow falls upon the centre of the moon's disc. The faint red- 
dish color, which the raocn exhibits in the midst of an eclipse, is 
supposed to proceed from the rays of light which are refracted by 
the earth's atmosphere, and fall upon the surface of the moon. 

An eclipse of the sun is caused by an interposition of the moon 
between the sun and the earth. See figure 1, of Plate VT. This 
can happen only at the new moon, or when the moon at the time 
of conjunction is near one of its nodes ; for unless the moon is 
in or near one of its nodes, it cannot appear in the same plane with 
the sun, or seem to pass over the sun's disc. In every other part 
of its orbit it will appear above or below the sun. Ifthemaoon 
is in one of its nodes, having no altitude, it will, in most cases, 
cover the whole disc of the sun, and produce a total eclipse ; if 
it be anywhere within about sixteen degrees of a node, a partial 
eclipse will be produced. 

When a bright lurainDUs ring appears round the dark body of the 
moon during an eclipse of the sun, it is called an annular eclipse. 
An annular eclipse is occasioned by the moon being at its greatest 
distance from the earth at the time of an eclipse ; in which situa- 
tion the vertex, or point of the cone of the moon's shadow, does not 
reach the surface of the earth. If the moon, when new, is in one 
of its nodes, the eclipse of the sun will be central; and if so, it v.ill 
also be annular, provided the distance of the moon from the earth 
at the time of the eclipse be greater than its mean distance. 

A total eclipse of the sun is a very curious and uncommon spec- 
tacle ; and total darkness cannot last more than three or four min- 
utes. Of one that was observed in Portugal more than one hun- 



10. Where are lunar eclipses risible ? 11. "When is a lunar eclipse par- 
tial ? 12. When total? 13. When central ? 14. To what is the faint 

reddish color of the moon, in tinieof its being eclipsed, owing? 15. How 

is an eclipse of the sun occasioned.' 16. Which figure represents it ? 

17. When can an eclipse of the sun happen ? 18. When will it be partial, 

and when total? iD. When is an eclipse of the sun annular? 2U. How 

18 it occasioned .'' 21. What is said of a central annular eclipse ? 



FIRST BOOK IN ASTRONOMY. 



75 



dred and fifty years ago, it is said that the darkness was greater 
than that of night ; that some of the largest stars made their ap- 
pearance ; and that birds were so terrified that they fell to the 
ground. A very remarkable total eclipse took place in New Eng- 
land, June 16, 1803. The day was clear; several stars were visi- 
ble; the beasts were greatly agitated ; and a gloom spread over the 
landscape. The first gleam of light contrasted with the previous 
darkness, seemed like the usual meridian day. On the 12th of 
February, 1S3J, was seen in various parts of the United States, an 
annular eclipse, u'hich awakened a most intense feeling of curi- 
osity. The types of this eclipse may be seen in the annexed wood 
cuts. 



Appearance of the sun. at the 
greatest obscuration, at Natches, 
Nashville, Washington, Baltimore, 
Philadelphia, New York, New Ha- 
ven, Hartford, Boston, NewBedford, 
Portsmouth, Portland, and all other 
places where the sun was about 
11^ digits eclipsed on his S. limb. 



Appearance of the sun, at the ap- 
parent conjunction of the sun and 
moon, in the Eclipse of the 12th of 
February, at Petersburg, Va. Ca- 
hawba, Siasconset, Halifax, and all 
other places where the sun was cen- 
trally, or very nearly centrally 
eclinsed. 




Eclipses were formerly beheld by mankind with terror and amaze- 
ment ; and were looked upon as prodigies which portended calamity 
and misery. Such fears and the erroneous opinions that produced 
them, originated in ignorance. The illiterate, in all ages, have 
beheld eclipses with a kind of terror: and, not having been able to 
account for the obscuration of any of the celestial bodies, super- 



2"2. Wiiat is Slid o: a totil eclipse of the sun which happened in Portu- 
gal? 23. And of that wliich took 'place in New-England in ]>Ut5? 



24. And of th tt which took place February 12th, li3l ? 



At what places 



in the United States was it annular ? 2o. How were eciipses fnnnerly 



considered .'- 



27. Wii.it is s.iid of the illiterata in relation to t!ie:ii 



76 FIRST BOOK IN ASTRONONY. 

stition has invented a thousand ridiculous stories to account for 
this seeming wonderful phenomenon. 

The natives of Mexico keep fasts during eclipses, imagining 
the moon has been wounded by the sun in a quarrel. Other nations 
have thought, that in an eclipse of the sun, that body has turned 
away its face with abhorrence from the crimes of mankind ; and, 
by fasting, they think to appease the excited wrath. This ignorance 
and superstition were greatly serviceable to the celebrated naviga- 
tor, Columbus. 

When he arrived at St. Domingo, on his fourth voyage of discov- 
eries, in the year 1502, he had the mortification to find the Spanish 
governor, who resided there, would not allow his ships to anchor, 
because he was jealous of the favors which Columbus had received 
from Isabella, then queen of Spain. This obliged him to put to 
sea in search of some more hospitable harbor. After he had 
searched in vain for a passage to the Indian ocean, he returned, 
and was shipwrecked on the coast of Jamaica. 

Being driven to great distress, in consequence of the natives 
withholding a supply of provisions, he had recourse to a happy ar- 
tifice, which not only produced the desired success, but heightened 
the favorable ideas the Indians had originally entertained of the 
Spaniards. By skill in astronomy he knew there would shortly be 
an eclipse of the moon. He assembled all the principal persons of 
the district the day before the eclipse happened ; and having re- 
proached them for their caprice, in withholding their assistance 
from men whom they had so lately and so highly respected, he 
told them the Great Spirit was so offended, at their want of human- 
ity to the Spaniards, that as a sign he intended to punish them with 
extreme severity, and that his vengeance was ready to fall on them, 
he would cause the moon, that very night, to conceal its light, and 
appear of a bloody hue, the certain emblem of Divine wrath. 

This artifice was a most successful one. It led to the speedy 
supply of all his wants. Some of these poor ignorant creatures did 
indeed hear his threat with indifference, while others listened to it 
with a degree of astonishment ; but when the moon began gradu- 



28. And of the natives of Mexico ? 29. Why did not the Spanish gov- 
ernor of St. Domingo allow Columbus to remain at the island ? 30. Under 

what circumstances was he brought upon the island of Jamaica ? 31. Did 

the natives of Jamaica receive him kindly .? 32. By what means did he 

manage so as to induce them to furnish him with the needed supplies ? 
S3. How did they receive his threat ? 



FIRST BOOK IN ASTRONOMY. 77 

ally to be darkened, all were struck with fear. They immediately 
rail with consternation to their houses, and returned instantly, loaded 
with provisions. 

Plutarch mentions, that at Rome it was not allowed to talk pub- 
licly of any natural causes of eclipses, the popular opinion running 
so strongly in favor of their supernatural production, at least those 
of the moon ; for as to those of the sun, the Romans had some idea 
that they were caused by the interposition of the moon between 
the sun and the earth. It could not, however, be imagined that 
there could be any body to pass between the earth and the moon, 
which was thought must be the case, if the eclipses of that lumi- 
nary were produced by natural causes. 

An eclipse of the moon with us is an eclipse of the sun to the 
inhabitants of the moon ; because the portion af the moon which 
appears dark to us during an eclipse is actually deprived of the 
light of the sun, by the interposition of the earth. On this account 
the eclipsed portions of the moon are prevented from seeing a por- 
tion of the sun. The sun, therefore, appears eclipsed to them. 



PHENOMENA OF THE TIDES. 
LESSON XXXVI. 



The sea is observed to flow for a certain time from the east to- 
wards the west. In this motion, which lasts about six hours, the 
sea gradually swells ; so that entering the mouths of rivers, it drives 
back the waters towards their source. After a continual flow of 
six hours, the sea seems to rest for about a quarter of an hour ; it 
then begins to ebb, or retire back again from west to east for six 
hours more ; and the rivers again resume their natural course. 
Then, after a seeming pause of a quarter of an hour, the sea again 
begins to flow, as before, and thus alternately. This regular alter- 
nate motion of the sea constitutes the tides. 

The tides are occasioned chiefly by the attraction of the moon ; 
but are affected by that of the sun. There are two tides in about 



34. How were they affected when the eclipse began to appear ? 35. What 

does Plutarch say was not allowed to be done at Rome ? 36. How did 

the Romans think eclipses of the sun might be effected ?- 37. And of those 

of the moon what did they think ? -38. When will the sun be eclipsed to 

the inhabitants of the moon ? 

]. What regular motion is observed in the sea ? 2. For what length o( 

time doeB it flow back and forth .? 3. By what are the tides occasioned ^ 



78 FIRST BOOK IN ASTRONOMY. 

twenty-five hours ; and the time of high and low water is every day 
fifty minutes later than on the preceding day. The moon is sup- 
posed to draw the earth towards itself, and to act upon the solid 
parts of it in the same manner as if its whole weight were in a sin- 
gle point in or near the centre. Now the v/aters at any place over 
which the moon is passing, will be more attracted than the earth, and 
therefore will be heaped up under the moon. But the waters on 
the opposite side of the globe will be less attracted than the earth ; 
consequently, the earth is drawn away from them ; and they are 
heaped up, or in other words, it is high water there. 

When the waters are elevated at the side of the earth under the 
moon, and at the opposite side also, it. is evident they must recede 
from the intermediate points, and thus the attraction of the moon 
will produce high water at two places, and low water at two places, 
on the earth, at the same time. In figure 4, of Plate VII, let S 
represent the sun, M the moon, and A B C D the earth. Here it 
will be seen that at A and B, the points of the earth nearest and 
most distant from the moon is a high tide, while at the intermediate 
points C and D, there is a corresponding depression, or low tide. 

The tide is fifty minutes later every day, because it is twenty- 
four hours and fifty minutes before the same meridian on our globe 
returns beneath the moon. The earth revolves on its axis in about 
twenty-four hours ; if the moon, therefore, were stationary, the 
same part of our globe would return beneath it, every twenty-four 
hours ; but as during our daily revolution the moon advances in its 
orbit, the earth must make more than a complete revolution in or- 
der to bring the same meridian opposite to the moon ; we are fifty 
minutes in overtaking it, and the tides are retarded for the same 
reason that the sun rises later on one day than on the preceding day. 

The tides, though constant, are not equal ; but are greatest when 
the moon is in conjunction or opposition with the sun, qr at the 
time of new and full moon ; and least when in quadrature. This 
increase and diminution constitute what is called the sj)i'ing and 



4. In what length of time are there two tides? 5. How does the time 

of high tide vary from day to day ? 0. How is the operation of the moon in 

causing the tides described, particularly that on the side of the earth most 
distant from the moon? 7. What mast evidently take place at the inter- 
mediate points, when the moon causes a high tide at the two opposite sides 

of the earth ? 8. How is figure 4, of Plate VII, illustrated? 1). Why 

i3 the tide fifty minutes later every day ? 10. How is this explained? 

11. Are the tides always of equal height ? 12. When are they highest? 

13. When least? 14. What is this increase and diminution of the tides 

called ? 



FIRST BOOK IN ASTRONOMY. 79 

neap tides. In figure 4, of Plate VII, will be seen exhibited tlie 
spring tides ; and in figure 5, of that Plate, will be seen the neap 
tides, w^here the effect of the moon's attraction on the earth in the 
production of them is partly counteracted by the attraction of the 
sun. 

The attraction of the sun does not raise tides ; its only effect is 
to increase or diminish those raised by the moon. The tides are 
highest when both luminaries are in the equator, and the moon at 
the least distance from the earth. This happens at the time of the 
equinoxes. The tide is at the greatest height, not when the moon 
is in the meridian, but sometime afterwards ; because the force by 
which the moon raises the tide continues to act after it has passed 
the meridian. The regular tides are greatly affected by strong 
winds. Continents also stop them in their course, and in narrow 
rivers they are frequently very high and sudden, on account of the 
resistance from the banks. 

The above, in connection with other minor causes, occasion a 
great diversity in the tides. Thus, upon the coasts of France, 
which border the British channel, the flux being confined in a ba- 
sin, and at the same time repelled by the coasts of England, rises 
to an enormous height ; at St. Maloss, even to fifty feet. The ordi- 
nary tide in the gulf of Hamburg is from six to eight feet ; but 
when the wind blows with violence from the northwest, the tide 
rises to 18 feet, sometimes even to more than 20 feet. In the bay 
of Fundy, actual observation has proved that tides rise at some 
points to the enormous height of seventy feet. 

In small collections of water, the moon acts at the same time on 
every part ; diminishing the gravity of the whole mass. On this 
account there are no tides in lakes, they being generally so small 
that when the moon is vertical, it attracts every part alike ; and by 
rendering all the waters equally light, no part can be raised higher 
than another part. The Mediterranean and Baltic seas have very 
small elevations, partly on the above account, and partly because 
the inlets by which they communicate with the ocean are so nar- 
row, that they cannot in so short a time either receive or discharge 
enough sensibly to raise or sink their surfaces. 

15. How are the spring and neap tides explained by the figures ? 16. At 

what periods in the year are tides the highest ? 12. Why is the high 

tide a short time afier the moon passes the meridian of a place .? 18. By 

what are the regular tides affected ? 19. What is said of the tides on the 

coasts of France which border on the British channel ? 20. And in the 

gulf of Hamburg ? 21. And in the bay of Fundy ? 22. Why are the 

tides small in lakes and other small collections of water .'' 23. Why are 

they small in the Mediterranean and Baltic seas ? 



.80 FIRST BOOK IN ASTRONOMY. 

From the resistance of the banks, in narrow rivers, the tides rise 
to a great height. In the river Severn, it is high water at the mouth 
of it and at London, while it is low tide between those places. A 
similar phenomenon is exhibited in the river Amazon, of South 
America. Here are to be seen no less than seven high tides in the 
course of five hundred miles, the distance to which the tide ascends, 
wdth low water between each one of them. 

Kepler was the first who ascertained that the tides are occasioned 
by the attraction of the moon. The great Newton, as in other de- 
partments of science, pursued the hint thus given, and has reduced 
this interesting subject to a perfect system. To the philosophical 
mind the tides appear as evincing wisdom and goodness in the 
Deity which should excite our love and admiration. Were it not 
for this constant motion the vast ocean might become stagnant, and 
the great fountain of contagion and death. 



ATMOSPHERE AND WIND. 
LESSON XXXVII, 



The air in which we live surrounds the earth to a considerable 
height,-revolves with it in its diurnal and annual motion, and, to- 
gether with the clouds and vapors that float in it, is called the at- 
mosphere. The height to which the atmosphere extends has never 
been ascertained ; but at a greater height than forty-five miles, it 
ceases to reflect the rays of light from the sun. The air is invisi- 
ble because it is perfectly transparent ; but it may be felt on moving 
the hand in it, or when it moves and produces what we call wind. 

The air is found on experiment to be about nine hundred times 
lighter than water. The weight of a column of air reaching from 
the top of it to the surface of the earth, is known to be equal to a 
column of water of the same size, thirty-three feet high, for that 
is the height to which water will rise in a pump. On the surface 



24. What is said of tides in narrow rivers ? 25. In the river Severn ? 

26. In the river Amazon ? 27. Who first ascertained that tides were 

occasioned by the moon's attraction ? 28. Who made improvements on 

his discovery ? 29. How does the Christian philosopher view the tides ? 

30. What would be the consequence were it not for them? 

1. What composes the atmosphere ? 2. To wliat height does it rise ? 

3. Why is it invisible ? 4. How may it be felt r 5. How much lighter 

than water is it ? 6. How is the weight of the air determined ? 



FIRST BOOK IN ASTRONOMY. 81 

of the earth the pressure of the atmosphere, upon every square inch 
is fifteen pounds. It has been computed that the pressure of the 
atmosphere on the whole surface of the earth is equal to a globe of 
lead sixty miles in diameter. We find no inconvenience from this 
great weight, because the pressure is alike on every part. 

Although the atmosphere is the great reservoir for the numerous 
vapors and effluvia which float about us, still without it vegetable 
and animal life could not exist. Insinuating itself into all the pores 
of bodies, it becomes the great spring of almost all the mutations 
ill material nature of which we are the witnesses. Without it the 
constitutions and principles of matter would be totally changed. 

As a proof that atmospheric air is necessary for the support of 
animal life, it may be mentioned that animals put under the re- 
ceiver of an air-pump soon expire when the air is extracted. If a 
number of persons are met in a small apartment, they soon find an 
inconvenience from the want of fresh air, unless by the opening of 
doors or windows a fresh supply can be admitted. Some years 
since, the Nabob of Calcutta confined, for a night, one hundred and 
forty-six Englishmen in an apartment called the Black-hole, but 
only twenty-three of them survived till the next morning. 

Were the atmosphere not elastic, but everywhere equable, its 
height would be determined from its density. By this means it 
would appear to be about fifty-five miles in height ; but the air be- 
ing very elastic, and the more it is compressed, the less space it 
occupies, it follows that in the upper regions, as it ascends, it must 
become more rarefied, till it extends to an immeasurable, or com- 
paratively infinite height. At the height of three and a half miles 
the density of the atmosphere is twice as much rarefied as at the 
earth's surface ; and at seven miles elevation, four times as much; 
and so on in a geometrical progression. 

Air is also the medium through which sound is conveyed to us. 
The organs of speech, or any sonorous body, make an impression 
on the air, and that is conveyed to the ear. The particles of air 

7. On the surface of the earth what is the amount of its pressure to a 
square inch ? 8. What has been the estimated amount of the whole pres- 
sure of the atmosphere upon the earth? 9. Why do we find no inconveni- 
ence from the pressure of the atmosphere ?■ 10. Of wliat use is the atmos- 
phere? 11. How is it shown that the atmosphere is necessary to the sup- 
port of animal life ? 12. What is the consequence if a number of persons 

be confined in a close small room? 13. What took place at Calcutta ? 

14. Under what circumstances might the height of the atmosphere be accu- 
rately determined ? 15. At what height is its density only half of what it 

is at the surface of the earth ? 16. At what height is it only a quarter of 

that density ? 17. How is sound produced ? 

L 



82 FIRST BOOK IN ASTRONOMY. 

set in motion by a sounding body communicate that motion to those 
next to them, those particles to others, and so on, until the particles 
of air are reached which are within the drum of the ear. The air 
then acts upon that membrane by communicating to it its own 
vibrations, which are transmitted to the auditory nerve, and by that 
nerve to the brain. Hence results the sensation of sound. 

As the air is a fluid, its natural state is undoubtedly that of rest, 
which it endeavors always to keep, or to retrieve, by an universal 
equilibrium of all its parts. When this equilibrium of the atmos- 
phere is destroyed in any part, there necessarily follows a motion of 
all the circumjacent air towards that part to restore it; and it is 
this motion of the air which is called wind. Wind may be pro- 
duced by a variety of causes ; but the most general are these two — 
heat and cold. Heat rarefies and expands the air, making it lighter 
in some places than it is in others, and cold by condensation makes 
it heavier. 

There are some winds which blow constantly in the same direc- 
tion. Of this kind, there are two general currents of the atmos- 
phere — that which follows the course of the sun in the torrid zone ; 
and that flowing from the cold regions around the poles, towards 
the equator, which is chiefly felt in the temperate zones. Other 
winds are periodical, or blow at only certain periods of the day, or 
the year ; but these, as well as the constant winds, are chiefly con- 
fined to warm climates. 

The periodical winds, or raonsoons, as they are denominated, pre- 
vail chiefly in the Indian ocean, blowing six months from the south- 
east, and then from the northwest the same length of time. The 
change of the periodical winds from one to a contrary direction, is 
generally attended with severe storms of thunder and lightning, 
and sometimes with hurricanes. These winds extend over the 
whole of India and the sea coast of East Persia. 

In islands and places near the sea in warm climates, particularly 
between the tropics, there is usually a wind blowing during the lat- 
ter part of the night and the forenoon from the land to the water ; 
and during the latter part of the day and the first part of the night, 
from the water to the land. These are called land and sea breezes. 

18. What is the natural state or tendency of the almospliere ? 19. What 

is the consequence when its equilibrium is destroyed? 20. How doe.s heat 

and cold tend to produce wind ? 21. What two constant winds are there ? 

22. What are periodical winds .^ 23. Where do they mostly prevail.^ 

24. What takes place when they change their direction .' 25. What 

winds are common on islanda and places near the ocean .' 26. W^hat are 

they called ? 



PIRST BOOK IN ASTRONOMY. 83J 

The most dreadful of all storms is that called a hurricane, with 
which hot countries are sometimes afflicted. It is a sudden and 
violent storm of wind, rain, thunder, and lightning, attended with 
a furious swelling of the sea, and sometimes with an earthquake ; 
in short, with every circumstance which the elements can assemble, 
that is terrible and destructive. Hurricanes are most frequent in 
the West Indies. 

The qualities of winds are affected by the countries over which 
they pass; and they are sometimes rendered pestilential by the 
heat of deserts, or the putrid exhalations of marshes and lakes. 
Thus from the deserts of Africa, Arabia, and the neighboring 
countries, a hot wind blows called the Samiel or Simoon, which 
sometimes produces instant death. A similar wind blows from 
the Sahara, upon the western coast of Africa, called Hermattan, 
producing a dryness and heat which are almost insupportable, and 
scorching like the blasts of a furnace. 

The velocity of wind, in a small breeze, is about four miles an 
hour ; in a fresh gale, twenty or thirty miles an hour ; in a violent 
storm, fifty or sixty miles an hour ; and in a hurricane, from eighty 
to an hundred miles an hour. 



TEMPERATURE OF THE ATMOSPHERE. 
LESSON XXXVIII. 

The presence of the sun is undoubtedly one of the principal 
sources of heat, as its absence is of cold ; but if those affections 
of the atmosphere depended solely on these two causes, an equal 
temperature would, at the same seasons, prevail in all places situ- 
ated under the same parallels. This, however, is far from being 
the case ; for the temperature of the eastern coasts of America is 
far colder than that of the western shores of Europe, in the same 
latitudes ; and the same observation may, with some degree of va- 
riation, be extended to the whole of these two continents. 



27. What are hurricanes ? 23. Where do they mostly prevail ? 

29. How are the qualities of winds affected ? 30. What is said of the wind 

called Samiel or Simoon ? 31. And of that called Hermattan .' 32. What 

is the velocity of wind in a small hreeze ^ 33. In a fresh gale .' 34. la 

a violent storm ? 35. In a hurricane 1 

1. What is a'principal cause of heat and of cold ? 2. If the sun were the 

only cause of heat what would be the consequence ? 3. What instances 

are named of places in the same latitudes having a different temperature ? 



84 FIRST BOOK IN ASTRONOMY. 

It is equally observable, that the tropical heats of Africa are far 
greater than those of the West India Islands, and some other parts 
of America, situated in the torrid zone; and indeed, an abundance 
of proofs might be adduced to show that the temperature of the 
air in different countries depends on a variety of circumstances be- 
sides geographical position. 

One great source of heat exists in the earth ; but whether this 
arises from any central fire, or from elementary heat diffused through 
the whole mass, is a problem of no easy solution. The warmth 
which the earth imparts to the atmosphere, tends greatly to moder- 
ate the cold ; and it has, by various observations, been found that 
the same degree of heat exists in all subterraneous situations at the 
same depth, or at least, that the variations are extremely small. 
The condensation of vapor also is another cause of heat, of which, 
it is well known, that vapor contains a great quantity. This con- 
densation is often formed by the attraction of an electrical cloud, 
and hence arises that sultry heat which in summer is often felt be- 
fore rain, and particularly before a thunder storm. 

As the earth is the source of heat, distance from the earth must, 
consequently, be a cause of cold ; and, in confirmation of this the- 
ory, it is invariably found that cold increases in proportion to our 
elevation in the atmosphere. Hence we find, even under the equa- 
tor, mountains of a certain height have their tops covered with 
snow. An elevation of 500 yards produces the same effect as a 
distance of 5,000^ miles from the equator. Accordingly, at an ele- 
vation of 13,000 feet we find the frosts of the frozen zone ; and at 
15 and 16,000 feet, the mountains, based upon the most scorching 
plains, are capped with perpetual snow and ice. 

The heat of the atmosphere is further augmented by the accu- 
mulation of the sun's rays at the surface of the earth. The rays 
are then reflected into the air and to surrounding objects ; so that 
the reflected heat is often greater than the direct heat of the sun. 
On this account, the heat in valleys, where the heat is reflected by 
hills and mountains, is sometimes very great. In an elevated val- 



4. What is the first soui-ce of heat named besides the sun ? 5. What has 

been found as to the temperature of the earth on descending below the sur- 
face ? 6. What is said of the condensation of vapor as an instrument in 

affecting the temperature of the air ?• 7. How is this condensation formed ? 

8. How is this known ? 9. How is the temperature affected in rising above 

the surface of the earth ? 10. What is evidence of this? 11. How does 

an elevation above the surface compare with distance from the equator as to 

temperature ? 12. How isj temperature affected by the reflection of the 

Bun'sruys? 13. What is said of heat in valleys ? 



FIRST BOOK IN ASTRONOMY. 85 

]ey in Switzerland, the heat is so much increased by reflection, that 
in the centre there is a spot of perpetual verdure, in the midst of 
perpetual snow and glaciers ; and there are plains on the Himma- 
leh mountains, 15,000 feet above the level of the sea, which pro- 
duce fine pasturage; and at the height of 11,000 feet, which is 
above the region of perpetual snows on the Andes, in the same lat- 
itude, barley and wheat are known to flourish. 

From these and various other considerations, it is evident that 
some parts of the globe are, from the nature of the soil, and other 
topographical circumstances, exclusive of their geographical po- 
sition with respect to the equator and the poles, better adapted for 
the reception and communication of heat than several others in the 
same latitudes. Stones and sands cool and heat more readily, and 
to a greater degree than mould or clay. From this cause proceeds, 
in a great measure, the excessive heats in the sandy deserts of 
Arabia and Africa, and the intense cold of Terra del Fuego and 
other stony countries in high latitudes. 

Countries that are uncultivated and covered with wood, are much 
colder than those which are open and cultivated ; as the former pre- 
vent the access of the solar rays to the earth or to the snow which 
they may conceal, and also present a greater number of evaporating 
surfaces than the latter. To be convinced that the air of woody 
countries is rendered colder by the evaporation from the trees and 
shrubs, it is only necessary to observe that a thick shade of trees 
is cooler than the shelter of buildings. 

As the land is capable of receiving and retaining much more 
heat or cold, than water can imbibe, the vicinity of the sea is also 
a circumstance which considerably affects the temperature of the 
air. The sea therefore moderates the heat in warm climates, and 
the cold in higher latitudes. When the rays of the sun strike 
upon the water, they will penetrate six or seven hundred feet, if 
there be that depth ; and the heat will be diffused through the 
whole mass remaining till carried off by evaporation. Consequently 
in hot climates, the body of the ocean is much cooler than the 
land : and in cold ones it is warmer. 



14. Of a valley in Switzerland ? 15. And of some plains on the Him- 

maleh mountains ? 16. What is evident from the above and other con- 
siderations ? 17. What is said of stones and sand as affecting tempera- 
ture ? 18. By reference to what places is this confirmed ? 19. What 

is said of cultivated and uncultivated countries in relation to this subject .-' 

20. What is mentioned as proof that the evaporation from trees affects 

temperature? 21. What comparison is made between the land and water 

as affecting temperature ? 



86 FIRST BOOK IN ASTRONOMY. 

Thus, too, countries which abound with rivers, lakes, and 
marshes, are also less subject to the extremes of heat and cold, than 
those which are dry. Islands which participate in the temperature 
of the sea, are generally cooler in summer, and warmer in win- 
ter, than continents in the same parallels ; and in regard to the 
latter the same comparison will hold good between the maritime 
parts and the interior. The difference between the heat of the 
day and the night is also less at sea than on land, especially in low 
latitudes ; and consequently less in islands and maritime places 
than in countries remote from the coast. 

The irregular intersection of the surface of the earth, by seas 
and mountains, branching out in a thousand different directions, 
and exhibiting a variety of appearances, numerous and multiform, 
beyond all the ideas that imagination can conceive, may to a super- 
ficial observer appear fortuitous, and present to the eye of ignorance 
the view of an immense ruin ; but to the physical geographer, it 
points out the agency of an all-wise provident Hand, in the archi- 
tecture of an immense fabric. When the apparent irregularities 
on the surface of the globe are inspected with the eye of philoso- 
phy, they are found not only beneficial, but absolutely necessary to 
the welfare of the inhabitants. 



CLOUDS, RAIN, SNOW, AND HAIL. 

LESSON XXXIX. 

Clouds are a collection of misty vapors suspended in the air. 
These vapors consist of water, particles of earth, nitre, sulphur, 
salts, and all other substances which the heat of the sun, and the 
action of terrestrial bodies, cause to rise above the surface of the 
globe. The lightest clouds are seldom more than two miles in 
height ; the more dense range within one mile ; and the most 
dense, surcharged with electricity, generally float, within half a 
mile of the ground. 



22. What is said of countries abounding with rivers, lakes, and marshes ? 

23. What comparison is made between islands and continents? 24. 

So far as the temperature of day and night is affected, what is said concern- 
ing seas and lands ? 25. What is said of the physical irregularities on 

the face of tlie earth ? 

1. What are olouds ? 2. Of what do they consist ? 3. To what height 

do they extend ? 



riRST BOOK IN ASTRONOMY. 87 

Among the advantages afforded us by the existence of clouds, 
they serve as screens between the scorching rays of the sun and 
the earth. So intense oftentimes are these rays, that were they not 
thus obstructed, vegetable life could scarcely be sustained. In the 
less discoverable operations of nature, where the electric fluid is 
concerned, clouds have a principal share ; and particularly serve 
as a medium for conveying that subtile matter from the atmosphere 
to the earth, and from the earth to the atmosphere. 

The various colors and appearances of clouds are owing to their 
particular situation in regard to the sun, to the different reflections 
of the sun's rays, and to the effects produced on them by heat. On 
being run together, or condensed into drops by the influence of 
cohesive attraction, fall by their own weight, and are called rain. 

The annual average is about three feet in depth, to the whole 
surface of the earth. This quantity, however, is not very equally 
distributed. It is most abundant in tropical regions, and decreases 
in proportion to the distance from the equator to the poles. Within 
the tropics, the rains, like the winds, occur regularly at certain 
seasons of the year. In the northern tropic, they begin in April, 
and end in September. In the southern, they begin in September, 
and end in April. In the West Indies, the average is nearly 4,en 
feet, while at the parallels of seventy degrees of latitude, and up- 
wards, the annual stock is not above ten inches. In some coun- 
tries, as in Egypt, and a part of Peru and Chili, there is little or 
no rain. 

The economy of nature is very beautiful. Vapors arise from the 
seas, pass in clouds over the lands, and then, by their own weight 
descend upon the earth to water and to fertilize it. Dr. Halley at- 
tempted to estimate the vapor drawn from the Mediterranean, dur- 
ing one sunny day ; and by calculating the surface of that sea, 
and making an experiment on a small quantity of water, he was led 
to suppose that it might be at least 5,280 millions of tons. 



4. What are the uses of them ? 5, To what are the various colors and 

appearances of clouds owing ? 6. How is rain produced ? 7. What is 

the annual depth of rain on the whole surface of the earth ? 8. Is it. 

equally distributed? 9. Where is it most abundant? 10. What is said 

of the rains between the tropics? 11. When do they begin in the north- 
ern tropic ? 12. When in the southern tropic? 13. What is said of 

rain in the West Indies, and at the distance of seventy degrees of latitude ? 

14. In what places is there little or no rain ? 15. What quantity of 

water did Dr. Halley suppose was evaporated daily from the Mediterranean 



88 FIRST BOOK IN ASTRONOMY. 

It has been supposed by Sir Richard Phillips, that the quantity 
of rain falling upon particular portions of the earth might be varied 
by artificial means. According to his hypothesis, the leaves of 
vegetables and particularly of trees, disturb the electricity of the 
clouds, and cause it to rain. Hence he concluded that more per- 
fect metallic conductors raised to greater heights in the atmosphere 
might be so combined as toproduce more certain results. 

Pursuing this idea, he traces to the cutting down of trees in civ- 
ilized countries their ultimate sterility, and conceives that to this 
cause solely is to be ascribed the present sterility of Syria, Chaldea, 
and Barbary, once the most fertile regions in the world ; and he 
ascribes the oases of the deserts to the circumstance of a few trees 
being accidentally suffered to grow on them. He imagines, that 
those countries might now be restored by erecting on their elevated 
surfaces a sufficient number of metallic rods to arrest the clouds 
and produce sufficient rain to sustain vegetation, and refill the 
almost exhausted rivers. 

As fanciful as this theory of Sir Richard appears, it is confirmed 
by what is taking place in nature. Thus, the first lands over which 
prevailing winds blow from the ocean are always the best watered ; 
and those farther off are less watered in proportion to their distance. 
The western countries of Ireland, Ireland itself with respect to 
England, and the western counties of England with reference to the 
eastern ones, prove the- powers of the innumerable spicula of veg- 
etation and minerals to disturb the electricity of the clouds, and 
make them fall in rain. From like causes, according to Sir William 
Young, the value of estates in several of the West India Islands 
has been greatly diminished by the cutting down of the trees. The 
phenomena of Peru and Chili, in the neighborhood of the elevated 
natural conductors of the Andes, Vv'here it rains almost perpetually, 
afford also a lesson to man, whenever the state of society enables 
him to adopt it. 

Clouds being condensed into drops by cohesive attraction, and 
then congealed or frozen by the cold as they are falling to the 
ground, produce what is called hail. 

16. What did Sir Richard Phillips suppose as to the quantity of rain? 

17. How did he suppose it might be done ? 18. What does he say of cut- 
ting down trees.' 19. What cases of illustration does he mention.' 

20. To what does he attribute the oases of deserts .'' 21. How does he 

suppose that steril countries might be restored to fertility .' 22. Is the 

theory of Sir Richard probable.' 23. What reason is mentioned in favor 

of it.^ 24. What is said of Ireland and England in support of this theory? 

2.5. What fact is affirmed relating to the subject from Sir William Young .-* 

2G. Of Peru and Chili what is said in confirmation of this theory .? 27. How 

is hail produced .' 



FIRST BOOK IN ASTRONOMY. ^ 

Natural historians furnish accounts of surprising showers of 
hail, in which the hailstones were of extraordinary magnitude. 
Dr. Halley mentions one, which occurred in the north of England, 
1697, killing fowls and other small animals, spliting trees, knock- 
ing down men and horses, and even ploughing up the earth to a 
considerable depth. The hailstones were of various forms, some 
of them weighing five ounces, and a few even half a pound. 
Another occurred five days later, even more disastrous. In this 
the hailstones were much larger than the other, and killed several 
persons, their bodies being beaten in a most shocking manner. 

Different particles of clouds touching each other, and freezing 
without being condensed into drops, produce what is called snow. 
In Lapland, Siberia, and other northern regions, snow falls to the 
depth of ten and twelve feet. By this means, as it is a preserva- 
tive against the effects of the frost, vegetable substances are kept 
alive to adorn the season of summer. In Labrador, during winter, 
the natives make houses under the surface of the snow, where they 
reside. Capt. Cartwright and the Moravian Missionaries describe 
them as warm and comfortable habitations. 

In Sicily, Naples, and Malta, the inhabitants preserve snow, and 
use it to cool their wines and other drink, as we do ice. It is kept 
in the caverns, in Mount I^na and other high mountains, so as to 
be secure from melting in that mild climate. The Sicilians carry 
on considerable trade in snow, which affords employment to some 
thousands of mules, horses and men. 



THEORY OF THUNDER AND LIGHTNING. 

LESSON XL. 

The surface of the earth, and of all bodies Vv'ith which we are 
acquainted, is supposed to contain or possess a power of exciting 
or exhibiting a certain quantity of an exceeding subtile agent, called 
the electric fluid. The quantity usually belonging to any surface 
is^called its natural state, and it then produces no sensible effects; 



28. What account does Dr. Halley give of a hail storm ? 29. How is an- 
other hail storm described, said to be still more disastrous ? 30. How is snow 

produced ? 31. What is said of snow in Lapland, Siberia, and other northern 

regions ? 32, What is the use of snow ? 33. What is said of it in Labra- 
dor ? 3-1. What is said of it in Sicily, Naples, and Malta? 

1. What is electricity ? 2. What is the natural state of a body when spoken 

of in relation to electricity ? 

M 



90 FIRST BOOK IN ASTRONONY. 

but when any surface becomes possessed of more, or less, than its 
natural quantity, it is electrified, and it then exhibits a variety of 
peculiar and surprising phenomena ascribed to the power called 
electric. 

If you take a stick of sealing-wax and rub it on the sleeve of 
your coat, it will have the power of attracting small pieces of paper, 
or any other light substances, when held near them. If a clean 
and dry glass tube be briskly rubbed with the hand, or with a piece 
of flannel, and then presented to any small light substances, it will 
immediately attract and repel them alternately for a considerable 
time. The tube is then said to be excited. If an excited glass 
tube, in a dark room, be brought within about half an inch of the 
finger, a lucid spark will be seen between the finger and the tube, 
accompanied with a snapping noise, and a peculiar sensation of 
the finger. Dry flannel clothes, when handled in the dark, fre- 
quently exhibit a sparkling appearance, attended with the same 
kind of noise that is heard in the experiment of the glass tube. 

When any body is possessed of more than its natural quantity of 
electricity, it is said to be positively electrified ; and when possessed 
of less than its natural quantity, it is said to be negatively electrified. 
If two substances come in contact, one charged positively and the 
other negatively with electricity, so much of the fluid passes from 
the former to the latter, as to produce an equilibrium. Certain 
bodies have the power of transmitting electricity from one surface 
to another, and are hence called conductors ; others not possessing, 
this power are called non-conductors. Metals, ores, and fluids in 
their natural state, excepting air and oils, are conductors ; vitrified 
and resinous substances, amber, sulphur, wax, silk, cotton, and 
feathers, are non-conductors. 

From the similarity between lightning and the electric fluid, it 
had long been supposed, that they were one and the same thing ; 
but it was left for Dr. Franklin to prove the truth of this supposi- 
tiori. When the clouds and the different terrestrial objects, over 
which they pass, are charged, one positively and the other negative- 



3. When is a body said to be electrified ? 4. V'hat experiment is made 

Tvith the sealing-wax ? 5, What one with a glass tube ? 6. "What is said 

of dry flannel clothes in illustration of the subject ? 7. When is a body'pos- 

itively electrified ? 8. When is it negatively electrified ? 9. What takes 

place when two substances come in contact, one charged positively and the 

other negatively ? 10. What substances are called conductors ? 11. Why 

are they so called ? 12. What ones arc called nonconductors? 13. Why 

are they so called ? 14. Who first proved that lightning and electricity aie 

the same thing ? 



FIRST BOOK IN ASTRONOMY. 91 

ly, in the passage of this fluid from the former to the latter, there 
is presented what we call lightning. So likewise, where two clouds 
come in contact, differently charged, the same result takes place. 
Thunder is the report which accompanies the taking place of this 
electrical union. It is occasioned by the rarefaction or displacinsr 
of the air, and its sudden return to its original position. Thunder 
and lightning bear the same relation to each other, as the flash and 
report of a cannon. 

The experiment of Dr. Franklin, to prove, that lightning and 
electricity were the same thing, was exceedingly simple. He took 
a boy's kite covered with a silk handkerchief instead of paper, and 
then fastened some wire to the upper part which served to collect 
and conduct the fluid. When he had raised this machine into the 
atmosphere, he drew electric fluid from the passing clouds, which 
descended through the flaxen strings of the kite as a conductor, 
and was afterwards drawn from an iron key, which he tied to the 
line at a small distance from his hand. This important discovery 
immediately led to the formation of conductors to secure buildings 
from the effects of lightning. Thunder is more or less intense, and 
of longer or shorter duration, according to the quantity of air acted 
upon, and the distance of the place where the report is heard from 
the point of the discharge. 

In summer when the earth is dry, and the day is warm, droughty 
and serene, the atmospheric electricity increases from sunrise till 
mid-day, when it arrives at its maximum ; it then remains stationary 
for two hours, and afterwards dinnnishes until the fall of the dew. 
Towards midnight it revives, to be again almost entirely extinguish- 
ed. In winter, the maximum of electricity is at eight o'clock in 
the evening, being weaker through the day. In all these variations 
atmospherical electricity seems very exactly to follow up the devel- 
opment of hydrogen gas, which is more or less considerable at differ- 
ent periods of the day. 

Electrical phenomena are more prevalent in some quarters of the 
globe than others. Towards the poles, the disengagement of hy- 

15. How is lightning produced ? 16. What is thunder ? 17. How is it 

caused? IS. To what is the relation between thunder and lightning com- 
pared r 19. With what experiment did Dr. Franklin make the discovery that 

lightning and electricity are the same ? 20. To what did his discovery lead ? 

21. By what is the duration and intensity of thunder affected ? 22. What 

is said of electricity in the season of summer r 23. And in winter ? 24. Iq 

these variations what is it said that atmospherical electricity exactly follows > 

25, _\pe electrical phenomena equally prevalent in all quarters of the 

globe ? 



92' FIRST BOOK IN ASTRONOMY. 

drogen gas is extremely scanty, and there is also no continual fric^ 
tion between the earth and the atmosphere. Thunder, accordingly, 
is rarely observed in those regions ; it is only a weak decrepitation. 
As we advance towards the equator, hydrogen gas becomes more 
abundant, and at the same time storms are most violent. It is under 
the equinoctial line that we meet with that vast extent of sea, where 
thunder storms almost constantly prevail. 

Storms, notwithstanding the calamities which they frequently 
occasion, and which the thunder rod cannot infallibly prevent, 
deserve to be considered as one of the greatest benefits our Creator 
has bestowed. They diffuse freshness through the atmosphere 
when it is in a confined and sultry state ; the plants resume their 
lively green, the flowers raise their drooping heads, when their 
thirst has been quenched by the rain ; the crops and fruits pene- 
trated by new warmth, ripen more rapidly, and man silently adores 
the great Being whose power has been displayed. 



EXPLANATION OF THE RAINBOW. 

LESSON XLI. 

The Rainbow is a meteor in form of a party colored arch, or 
semicircle, exhibited only at the time when it rains. It is always 
seen in that point of the heavens which is opposite to the sun, and is 
occasioned by the refraction and reflection of the sun's rays in the 
drops of falling rain. There is likewise, though not always dis- 
tinctly visible, a secondary rainbow, much fainter than the primary 
one, and at some distance from it. 

The different colors of the rainbow are owing to the refraction 
and reflection of the sun's rays thus produced. These colors ap- 
pear the more vivid, as the clouds which are behind them are 
darker, and the drops of rain fall closer. The drops continually 
forming produce a new rainbow every moment, and as each spec- 
ator observes it from a particular situation, it happens that scarce- 
ly two men, strictly speaking, see the same rainbow; and this 
appearance can only last whilst the drops which fall are succeed- 
ed by others. 

26. What is said of them in polar regions ? 27. And in the equatorial re- 
gions ? 28. What is said of storms ? 29. What advantage results from 

them ? 

1. What is the rainbow ? 2. In what part of the heavens is it seen .' 

3. What is said of the secondary rainbow ? 4. To what are the colors of the 

rainbow owing ? 5. Do different persons see the same rainbow ? 



FIRST BOOK IN ASTRONOMY. 93 

As evidence that rainbows are occasioned in the manner stated, 
it may be observed that artificial rainbows are easily produced. 
Cascades and fountains, whose waters, in their fall, are divided 
into drops, will exhibit rainbows to a spectator, properly situated, 
during the time of the sun's shining. This appearance is also 
seen by moonlight, though seldom sufficiently vivid to render 
the colors distinguishable. Colored bows have been seen on 
grass formed by the refraction of the sun's rays in the morning 
dew. 

Artificial rainbows may also be produced by a candle light on 
the drops of water ejected by a small fountain. But the most 
natural and pleasing is by means of the air fountain, the jet of which 
is perforated with a great number of very fine holes from which the 
water spouts so as to form a kind of fluted column. The rainbow 
is formed by the sun's rays, for the spectator has only to place the 
spouting streams directly in the sun's beams, with his own back 
to the sun, and being in a direct line with the sun • and the centre 
of the jet, by stooping his head to a certain degree, he will discover 
the beautiful appearance of the natural prismatic colors, and a 
small rainbow, on the same principle as those which are seen in 
the time of rain and sunshine. 



PARALLAX OF THE HEAVEJNTLY BODIES. 

LESSON XLII. 

The parallax is an arc of the heavens intercepted between the true 
place of the moon , or any other heavenly body, and its apparent 
place. The true place of the moon, or star, is the point of the 
heavens in which it would be seen by an eye placed in the centre 
of the earth. And the apparent place, is that point in the heavens 
where the moon, or star, appears to an eye on the surface of the 
earth. 



6. Can artificial rainbows be produced ? 7. What is said of those produced 

by cascades ? 8. What is said of them when seen by moonlight? 9. And 

of the colored bows seen on the grass ? 10. How may artificial rainbows 

be produced by candle-light ? 11. How are the most natural and pleasing 

ones produced ? 12, How is the appearance described ? 

1. What is the parallax of a heavenly body ? 2. What is the true place of 

the moon or a star ? 3. What is the apparent place of it r 



94 FIRST BOOK IN ASTRONOMY. 

In figure 9 of Plate VIII. to a spectator at G the centre of the 
earth, the moon at E would appear among the stars at I ; but 
seen from A on the surface of the earth, it would appear at K. 
The place I is its true situation, and K its apparent situation ; and 
the difference between them is its parallax. 

The parallax is greatest when the heavenly body is in the hori- 
zon, and decreases as the body ascends towards the zenith, at 
which place it is nothing. Thus it may be seen, from the figure 
named in the preceding paragraph, that when the moon rises above 
the horizon to D, it will have a less parallax than when at E ; and 
when at the zenith F, there will be to it no parallax. 

The nearer a body is to the earth the greater is its parallax ; 
hence the moon on this account has the greatest parallax, and the 
fixed stars, from their immense distance, have no parallax, the 
semidiameter of the earth appearing at that distance, no more than a 
point. Thus, if the moon were at the small e, the parallax would 
be less than if it were at the capital E. 

What is termed annual parallax is the difference . in the appar- 
ent place of a heavenly body, as seen from opposite points in the 
earth's orbit. This orbit is about one hundred and ninety millions 
of miles in diameter. Hence an object, unless immensely distant 
as seen from one part, must appear in a very different place in the 
heavens, from the same object as seen from the opposite part. 

It is seen, from what is said above, and from the lesson on the 
refraction of light, that refraction and parallax both make bodies 
appear where they are not ; but refraction elevates them and par- 
allax depresses them. They are both greatest in the horizon, and 
vanish entirely at the zenith. 



4. Which figure illustrates the parallax ? 5. How is the illustration given 

by the figure ? 6. Where is the parallax greatest? 7. How is it altered 

in rising above the horizon ? 8. How is this explained by the figure ? 

9. How is the parallax affected by distance from the earth ? 10. And how 

is this shown from the figure? 11. What is the annual parallax ? 12. 

What is said of bodies seen fi-om the earth in different parts of its orbit ? 

13. What comparison is made between refraction of light and parallax ? 



.ATEVUL. 



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FIRST BOOK IN ASTRONOMY. 9B 

PROBLEM I, ON THE TERRESTRIAL GLOBE. 

LESSON XLIII. 

The Method of finding the Latitude and Longitude of any given 

Place. 

Process. Find the given place on the globe, and bring it to the 
graduated edge of the biazen meridian. Then, the degree on this 
meridian, immediately over the place, will be the latitude sought y 
and the degree on the equator, which corresponds with the graduated 
edge of the brazen meridian, will be the longitude of the given place. 

Note. If the latitude is north of the equator, it is called north 
latitude ; if south of the equator, it is called south latitude. If the 
longitude is east of the first meridian, it is called east longitude j 
if west of the first meridian, it is called west longitude. 

QUESTIONS FOR PRACTICE. 

1. What is the latitude and longitude of Philadelphia ? 2. What is the 

latitude and longitude of the island St. Helena ? 3. What is the latitude and 

longitude of Quito ? 4. What is the latitude and longitude of Nankin ? - 

5. What is the latitude and longitude of Charleston, S. C. ? 6. What is the 

latitude and longitude of Cape Horn ? 7. What is the latitude and longitude 

ofBatavia? 8. Of Quebec? 9. Of Archangel? 10. OfGibralter? 

11. Of Buenos Ayres? 12. Of Calcutta ? 13. Of Mexico ? 14. Of 

Canton .' 15. Of the island of Chiloe .'' 16. What place has no latitude 

or longitude ? 



PROBLEM II, ON THE TERRESTRIAL GLOBE. 

LESSON XLIV. 

Method of finding the Difference in Latitude between any two given 

Places. 
Process. Bring the places successively to the meridian, and 
note the latitude of each. If the latitudes thus found be both north, 
or both south, subtract the less from the greater, and the remainder 
is the difference between them. If one of them be north latitude, 
and the other be south latitude, they are to be added together, and 
their sum is the difference required. 

QUESTIONS FOR PRACTICE. 

1. What is the difference between the latitude of Baltimore and Mexico ? 

2. What is the difference between London and Rome ? 3. What is the dif- 
ference between Boston and Buenos Ayres ? 4. Between Constantinople 

and Cape Town? 5. Between Lima and Philadelphia? 6. Between 

Canton and Paris ? 7. Between Quito and New Orleans ? 8. Between 

New York and Valparaiso ? 9. Between Archangel and St. Petersburg, iu 

Russia ? 10. Between Portland and St. Salvador ? 



9s FIRST BOOK IN ASTRONOMY. 

PROBLEM in, ON THE TERRESTRIAL GLOBE. 

LESSON XLV. 

Method of fueling the Difference in Longitude between any two 
given Places. 

Process. Find the longitude of each place, subtracting the less 
from the greater, if they be both east, or both west longitude, and 
the remainder will be the difference sought. If one place be east, 
and the other west longitude, tl:iey are to be added together, and 
the product will be the difference required. 

QUESTIONS FOR PRACTICE. 

1. What is the difference of longitude between Vienna and Calcutta: 

2. Between Cincinnati and Savannah ? 3. Between Boston and Rome ? 

4, Between St. Louis and New Haven ? 5. Between Lisbon and Genoa ? 

— — 6. Between "Warsaw and Dublin ? 7. Between Cork and Adrianople r 

8. Between Cadiz and Berlin ? 9. Between Baltimore and Cadiz? 

10. Between Copenhagen and Astrachan ? 11. Between Oporto and Bour- 

deaux .'' 12, Between London and Washington ? 



PROBLEM IV, ON THE TERRESTRIAL GLOBJ 

LESSON XLVI. 

The Method offnding a Place, ichen the Latitude and Longitude 

are given. 

Process. Look on' the equator for the given longitude, and 
bring it to the brazen meridian. Then find the given latitude on 
the meridian, and directly under it is the place required. 

QUESTIONS FOR PRACTICE. 

1. What city is situated thirty degrees east longitude, and thirty-one degrees 

north latitude .' 2. "V\'hat island lies six degrees west longitude, and sixteen 

degrees south latitude ? 3. What city is situated ninety degrees west longi- 
tude, and thiity degrees north latitude.^ 4. What one 116° east longitude, 

and 40° north latitude : 5. ^ATiat one 77° west longitude, and 12° south 

latitude ? 6. What island lies 5° west loncritude, and 16° south latitude? 

7. TMiat one 63° west, and between 32° and 33° north ? 8. What one 156° 

west, and 19° north ? 9. What one 121° east, and 15° north ? 10. What 

one 81° east, and 8° north ? 



PROBLEM V, ON THE TERRESTRIAL GLOBE. 

LESSON XLVII. 

Method of rectifying the Globe to the Latitude, to the Zenith, and 
to the Swi's Place. 

Process. Elevate the pole above the horizon, till its altitude is 
equal to the latitude of the place. If the place is in north latitude, 



FIRST BOOK IN ASTRONOMY. 97 

the north pole is to be elevated; if it is in south latitude, the south 
pole is to be elevated. When this is done, fix the quadrant of alti- 
tude on the brazen meridian, at the zenith, which is directly over 
the latitude of the place. The globe should also be placed so that 
the poles may stand due north and south, corresponding with the 
poles of the earth. 

The globe having been thus rectified to the latitude and the ze- 
nith, let the given day of the month be found in the outer circle of 
the wooden horizon, and against it, in the middle circle, is the sun's 
place in the ecliptic. Then find the same sign and degree in the 
ecliptic, bringing it to that part of the meridian numbered from the 
equator to the poles; at the same time putting 12 on the hour cir- 
cle to the said meridian. The globe is now rectified as required. 

EXAMPLES FOR PRACTICE. 

Let Ihe globe be rectified for New York on the loth of May. New York 
being about 40° north, the north pole must be raised 40° above the horizon, and 
the quadrant of altitude fastened directly over the latitude. Then find on the 
horizon the 15th of May, which answers to the twentieth of Taurus. This be- 
ing done, bring the twentieth of Taurus on the ecliptic, to the meridian, and 
Bet the index to the hour circle at 12, and the globe is rectified. For the lati- 
tude and zenith of all other places, the globe may be rectified in the same way. 
From a similar examination of the horizon to the globe, it will be seen the 1st 
of June corresponds to the 10th of Gemini ; the 10th of August to the 18th of 
Leo ; and the loth of April to the 26th of Aries. 

QUESTIONS FOR PRACTICE. 

1. How is the globe rectified to the latitude of a place ? 2. And to the 

zenith ? 3. And to the sun's place ? 4. Where is the sun's place on the 

ecliptic, on the 5th of July ? 5. On the 12th of January ? 6. On the 25th 

of December ? 7. On the 14th of September ? 8. 'On the 20th of May ? 

9. On the 4th of April ? 10. On the 22d of November ? 



PROBLEM VI, ON THE TERRESTRIAL GLOBE. 
LESSON XLVIII. 

The Method of finding the Distance between any two given Places. 

Process. Bring one of the places to the brazen meridian, over 
which fix the quadrant of altitude ; then extend it over the other 
place, and the number of degrees on the quadrant, contained be- 
tween, is the distance in degrees. This being done, multiply the 

N 



98 



FIRST BOOK IN ASTRONOMY. 



number of degrees by 691, and the product will be the number of 
English miles. If multiplied by 60, the product will be the num- 
ber of geographical miles. 

QUESTIONS FOR PRACTICE. 

I. What is the distance in English miles between Boston and New Orleans ? 

2. Between London and Paris ? 3. Between Vienna and Rome ? 

4. Between Philadelphia and Savannah ? 5. Between Pekin and Constan- 
tinople ? 6. Between Berlin and Madrid ? 7. Betweea Archangel and 

Moscow ? 8. Between Baltimore and Lexington, Ky. ? 9. Between New 

York and Montreal ? 10. Between Calcutta and Canton ? 



PROBLEM VII, ON THE TERRESTRIAL GLOBE. 
LESSON XLIX. 

The Method of finding the Hour of the Day at a required Place j 
when the Day and Hour at another Place are given. 

Process. Bring the given place to the meridian, set the index 
to the given hour ; then turn the globe till the required place comes 
under the meridian, and the index will point out what the hour is 
at that place. Thus when it is 12 o'clock, at noon, in London, it 
is 7 o'clock in the morning at Philadelphia; and 4 o'clock in the 
afternoon at the island Mauritius. 

QUESTIONS for PRACTICE. 

1. When it is 10 o'clock in the morning at Boston, what will be the hour at 

Cincinnati ? 2. When it is noon at Boston, what will be the hour at Paris ? 

3. When it is noon at London, what will be the hour at Constantinople? 

4. When it is noon at St. Petersburg, what will be the hour at New York ? 

5. When it is noon at Rome, what will be the hour at Canton ? 

6. When it is noon at Baltimore, what will be the hour at New Orleans? 

7. When it is noon in Boston, where is it midnight? 8. At Washington, when 

it is 6 o'clock in the evening, where is it noon r 9. When it is noon at Que- 
bec, what will be the hour at the m.outh of the Columbia river ? 



PROBLEM VIII, ON THE TERRESTRIAL GLOBE. 

LESSON L. 

Method of finding at ivhat Hour the Sun rises and sets, and, the 
Length of the Day and Night, at any Place, on any given Day 
of the Year. 

Process. Find the latitude of the place, and rectify the globe 
for the latitude ; find the sun's place in the ecliptic, bring it to the 
brazen meridian, and set the index of the hour circle at the upper 



FIRST BOOK IN ASTRONOMY. 99 

]2 ; tarn the globe on its axis eastward until the sun's place is level 
with the horizon, and the index will point to the hour of the sun's 
rising. Turn the globe on its axis westward, until the sun's place is 
level with the western edge of the horizon, and the index will point 
to the hour of the sun's setting. 

The hour of the sun's rising being doubled, shows the length of 
the night; and the hour of the sun's setting being doubled, shows 
the length of the day. 

QUESTIONS FOR PRACTICE. 

1. At what time will the sun rise and set at New- York, on the 20th of De- 
cember? 2. Wh^t will be the length of the day and of the night ? 3. At 

what time will the sun rise and set at Boston, on the 20th of September ? 

4. And what will be the length of the day and of the night ? 5. At what 

time will the sun rise and set, at St. Petersburg, on the lOth of January ? 

6. And what will be the length of the day and the night ? 7. At what time 

will the sun rise and set at London on the 22d of June ? 8. And what will 

be the length of the day and the night ? 9. At what lime will the sun rise 

and set at New Orleans, on the 5th of August ? 10. And what will be the 

length of the day and the night ? 



PROBLEM IX, ON THE TERRESTRIAL GLOBE. 

LESSON LI. 

Method of finding those Days of the Year on which the Sun will be 
Vertical at any given Place in the Torrid Zone. 

Process. Bring the given place to the brass meridian, and mark 
'its latitude ; then turn the globe on its axis, and observe those two 
points of the ecliptic, which pass under that degree of latitude; 
look for these points of the ecliptic, in the circle of signs on the 
horizon, against which, in the circle of months, are the days re- 
quired. 

QUESTIONS FOR PRACTICE. 

1. When will the sun be vertical at Calcutta ? 2. At Sierra Leone ? 

3. At Mexico ? 4. At Lima ? 5. At Canton ? 6. At Quito ? 7. At 

St. Helena ? S. At Rio Janeiro ? 9. At Havanna ? 10. At the Sand- 
wich Islands ? 11. At the Pelew Islands ? 12. At the Friendly Islands .' 



PROBLEM X, ON THE TERRESTRIAL GLOBE. 

LESSON LII. 

Method of finding all those places on the Globe which icill have a 
vertical Sun, the Month and the Day oj the Month being given. 

Process. Find the sun's place in the ecliptic, as directed in a 
previous problem, and bring it to the meridian; turn the globe 



100 FIRST BOOK IN ASTRONOMY. 

round, and all the places that pass under that degree of the merid- 
ian, will have a vertical sun on that day. 

QUESTIONS FOR PRACTICE. 

1. "What places will have a vertical sun on the twenty-second of February ? 

2. What ones on the tenth of June ? 3. What ones on the fourteenth 

of August? 4. What ones on the sixteenth of September? 5. What ones 

on the eighth of May ? 6. What ones on the fourth of July ?— — 7. What 

ones on the twentieth of November? 8. What seas will have a vertical 

sun on the ninth of May ? 9. What large i-ivers will be affected by a ver- 
tical sun on the first of June ? 10. What large rivers will be affected by a 

vertical sun on the first of March ? 



PROBLEM I, ON THE CELESTIAL GLOBE, 
LESSON LIU. 

The Method of finding the Latitude or Longitude of any gii^en Star. 

Process. Screw the quadrant on the pole of the ecliptic, bring 
the star to the meridian, and the degrees of the quadrant, between 
the ecliptic and star, show the latitude, and the degree of the eclip- 
tic under the graduated edge of the quadrant, is the longitude. 

Note. Latitude^ on the celestial globe, is reckoned from the 
ecliptic, north and south. Longitude is reckoned on the ecliptic, 
from the first point of Aries round the globe. 

QUESTIONS for PRACTICE. 

1. What is the latitude and longitude of Arcturus ? Ans. Latitude is 31° 

north ; longitude is 201°. 2. W^hat is the latitude and longitude of Regulus? 

3. Of Vega, in the Harp ? 4. Of Medusa's Head .? 5. Of Sirius ? 

6. Of Pollux, in Gemini? 7. Of Antares, in Scorpio? 8. Of Altair, in 

Aquila ? 9. Of Argol, in Perseus ? 10. And what is the latitude and 

longitude of Canis Minor ? 



PROBLEM II, ON THE CELESTIAL GLOBE. 
LESSON LIV. 

Method of finding the DecUfiation and Right Ascension of the Sun 

or a Star, 

Process. Bring the place of the sun or the given star to the 
brass meridian, and the degree above it will be its declination ; 
and the number of degrees on the equinoctial under the meridian, 
reckoning from Aries eastward, is the right ascension. 

Note. Declination is reckoned from the equinoctial, north and 
south. Right Ascension, is reckoned on the equinoctial from the 
first point of Aries round the globe. 



FIRST BOOK IN ASTRONOMY. 101 

QUESTIONS FOR PRACTICE. 

1. What is the declination and right ascension of the sun on the 19th of April ? 
Ans. Declination, 11° 19' ; right ascension, 27° 30'. 2. What is the declina- 
tion and right ascension of the sun on the 2d of December ? -3. On the 18th 

of February ? 4. On the 4th of March ? 5. On the lOih of May ? 

6. Of the star Rigel, in Orion ?-^ 7. Of Aldebaran, in Taurus ? 8. Of Ras- 

taben, in Draco ? 9. Of Algol, in Perseus r 10, Arcturus, in Bootes ? 



PROBLEM III, ON THE CELESTIAL GLOBE. 

LESSON LV. 

Method of finding the Place of a heavenly Body on the Globe, ivhen 
the Latitude and Longitude are given. 
Process. Place that part of the quadrant of altitude marked 0, 
on the given longitude in the ecliptic, and the upper end over the 
pole of the ecliptic ; and under the given latitude will be found 
the star required. 

QUESTIONS FOR PRACTICE. 

1. What is the star whose longitude is 201°, and its latitude 31° north ? Ans. 

Arcturus, in Bootes. 2. What star is that which has a longitude of 299°, and 

a latitude of 29° north ? 3. That which has a longitude of 85°, and a latitude 

of 16° south ? 4. That which has a longitude of 300° and a latitude of 44° 

north ? 5. That which has a longitude of 79° and a latitude of 32° north ? 

6. That which has a longitude of 334°, and a latitude of 21° south ? 7. That 

■which has a longitude of 107°, and a latitude of 10° north? 8. And that 

which has a longitude of QQ~°, and a latitude of 5^° south ? 



PROBLEM IV, ON THE CELESTIAL GLOBE. 

LESSON LVI. 

Method of finding the Place of a heavenly Body on the Ghbe, 
when the Right Ascension and Latitude are given. 
Process. Bring the given degree of right ascension to the 
graduated edge of the brass meridian, and note the degree. Then 
immediately under the given declination, on the brass meridian, 
will be found the place of the star required. 

QUESTIONS FOR PRACTICE. 

1. What is the star whose declination is thirty degrees and forty minutes south, 
and right ascension 341° 38' ? Ans. Formalhaut, in the southern Fish. 

2. What one has a right ascension of 129°, and a declination of 7° north ? 

3. What one has a right ascension of 83°, and a latitude of 34° south ? 

4. What one has a right ascension of 26°, and a latitude of 20° north .' 

5. What one has a right ascension of 54°, and a latitude of 23-|° north 1 

6. What one has a right ascension of 113°, and a latitude of 28^° north .' 

7. What one has a right ascension of 99°, and a latitude of 16-^° south ? 

8. What one has a right ascension of 76°, and a latitude of 8-|-° south ? 

9. What one has a right ascension of 46t°, and a latitude of 10° south .' 

10. What one has a right ascension of 110^°, and a latitude of 32° north ." 



102 FIRST BOOK IN ASTRONOMY. 

PROBLEM V, ON THE CELESTIAL GLOBE. 

LESSON LVII. 

MetJiod of finding the Distance in Degrees between any two given 
Stars on the Globe. 

Process. Lay the quadrant of altitude over the two given stars ; 
and the number of degrees between them as reckoned on the quad- 
rant, will be their distance as seen from the earth. Or, extend a 
thread over any two given stars ; apply the distance found to the 
equator, and count the number of degrees. 

QUESTIONS FOR PRACTICE. 

1. What is the distance between Altair, in the Eagle, and Sega, in Lyra ? 

2. Between Pollux, in Gemini, and Altair .-' 3. Between Spicaand Regula ? 

4. Between Castor and Pollux ? 5. Between Rigel and Aldebaran ? 

6. Between Sirius and Procyon ? 7. Between Arcturus and Procyon ? 

8. Between Vega and Rastaben ■* 9. Between Sirius and Deneb ? 10. Be- 
tween Regel and Sirius ? 



DICTIONARY OF ASTRONOMICAL TERMS. 



A. 



Aberration, is an apparent motion 
of the celestial bodies, arising from 
the progressive motion of light, and 
the earth's annual motion in its 
orbit. 

Absolute Equation, is the sum of 
the optic and eccentric equations. 

Acceleration. The diurnal Accelera- 
tion of the Fixed Stars, is the time 
which the stars, in one diurnal revo- 
lution, anticipate the mean diurnal 
revolution of the sun; which is 3° 
55' 9". 

Acceleration of a Planet. A planet 
is said to be accelerated when its real 
diurnal motion exceeds its mean diur- 
nal motion. 

Acceleration of the Moon, is a term 
used to express the increase of the 
moon's mean motion from the sun, it 
being somewhat greater now than 
formerly. 

Acherner, a star of the first mag- 
nitude, in the constellation Eridanus, 
right ascension, 22|°, Dec. 58° 17' S. 

Achronycal, is said of a star, or plan- 
et, when it is opposite to the sun. A 
star rises achronycally, when it rises 
at sunset ; and sets achronycally when 
it sets at sunrise. 

Acubene, a star of the fourth mag- 
nitude, in the southern claw of Can- 
cer, marked a. 

Acteraimin, a star of the third mag- 
nitude, in the left shoulder of Ceph- 
eus, marked a. 

Adhil, a star of the sixth magnitude, 
on the garment of Andromeda. 

Aldebaran, a star of the first magni- 
tude, in the sign Taurus. Right as- 
cension 4h. 25' 35". Dec. 16° 8'. 
This star frequently suffers an occul- 
tation by the moon, when the ascend- 
ing node is in Virgo. 

Aldhafera, a star of the third mag- 
nitude, in Leo. 

Algenib, a star of the second mag- 
nitude, on the right side of Perseus. 

Algol, or Medusa's Head, a variable 
star in the constellation Perseus. 



Algorab, a star of the third magni- 
tude, in the right wing of Corvus. 

Allioth, a star of the third magni- 
tude, in the tail of the Great Bear. 

Almacantars, are circles of altitude, 
parallel to the horizon. 

Almanac, a calendar, wherein the 
days of the month, festivals, lunation, 
motions of the heavenly bodies, 
eclipses, &c. are set down for each 
year. 

Alpheratz, a star of the second mag- 
nitude, in the head of Andromeda. 

Altitude of a Celestial Body, is the 
arc of a vertical circle, measured from 
the horizon. 

Amphiscii, or Arnphiscians , are the 
people who inhabit the torrid zone, 
so called because they have their 
shadows at noon, turned sometimes 
one way, and sometimes another, or 
north and south. 

Amplitude, is an arc of the horizon 
intercepted between the east or west 
point, and the centre of the sun or 
star, at its rising or setting. 

Analemma, is a projection of the 
sphere on the plane of the meridian 
made by straight lines and ellipses, 
the eye being supposed at an infinite 
distance, and in the east and west 
points of the horizon. 

Andromeda, a northern constella- 
tion, containing, according to Flam- 
stead, sixty-six stars. 

Angle, is the inclination of two 
lines, or planes, meeting in a point, 
and may be any quantity less thanl80°. 

Angle of Commutation, is the angle 
at the sun, formed by two lines, one 
drawn from the earth, and the other 
from the place of the planet reduced 
to the ecliptic, meeting in the sun's 
centre. 

Angle of Elongation, is the angle 
formed by two lines drawn from the 
earth, the one to the sun, and the oth- 
er to the planet, or it is the difference 
between the sun's place and the geo- 
centric place of the planet. 



104 



DICTIONARY OF 



Angle of Erection, is an inequality 
in the motion of the moon, by which, 
at or near her quadratures, she is not 
in the line drawn through the centres 
of the earth and sun, as she is at the 
syzygies, but makes an angle with 
that line of about 2° 51'. 

Angular Motion, is the motion of 
the planets about the centre of the 
sun, or it is that of the satellites about 
the centres of their primaries. 

Annual, yearly, something that re- 
turns or ends with the year. 

Anmial Argument, is an arc of the 
ecliptic comprehended between the 
sun's place and that of the moon's 
apogee. 

Annual Epact, is the excess of the 
solar year above the lunar, which is 
10 d. 21 h. 11m. or nearly 11 days, 
which shows that the moon changes 
so much sooner in any month of the 
subsequent year, than it did the year 
before. 

Annual Equation, is the difference 
between the planet's mean and true 
place. 

Anomalistical Year, is the time from 
the sun's leaving its apogee, till it re- 
turns to it again, which is 365 d. 6 h. 
15 m. 

Anomaly, is the distance of a planet 
in degrees, minutes, and seconds, from 
the aphelion or apogee. 

Anse, or Anses, signify the seem- 
ingly prominent parts of -the ring of 
Saturn, which are seen at its open- 

Antarctic Circle, is a small circle 
parallel to the equator, and 23° 28' 
from the south pole. 

Antarctic Pole, is the south pole, or 
the southern extremity of the earth's 
axis. 

Antares, the Scorpion's heart, a star 
of the first magnitude, in the constel- 
lation Scorpio. 

Antecedentia, a term made use of to 
signify that a planet moves retrograde, 
or contrary to the order of the signs, 
that is, from east to west. 

Antieci, or Antecians, are those who 
live under the same meridian, and at 
the same distance from the equator, 
but one having north, and the other 
south latitude. 

Antipodes, are the people of two 
places diametrically opposite to each 
other ; they differ in longitude 180°, 
and one has the same latitude north, 
as the other has south. 

Aphelion, is that point in the orbit 
of the earth or planet, which is at the 
greatest distance from the sun. 



Afogee, is that point in the moon's 
orbit, which is farthest from the 
earth. 

Apparent, that which is visible or 
evident to the eye. 

Apparent conjunction of the plan- 
ets, is when they have the same geo- 
centric longitude. The apparent con- 
junction of the moon with any of the 
heavenly bodies, is their conjunction 
as seen from the surface of the earth. 

Apparent diameter of the heavenly 
bodies, is their angular diameter, as 
seen from the earth, measured with a 
micrometer. 

Apparent distance of two celestial 
bodies, is their angular distance as 
seen from the earth. Apparent hori- 
zon is that circle which limits our 
sight, and has its plane parallel to 
the true horizon, passing through the 
centre of the earth. 

Apparent Place and Time. See 
Place and Time. 

Appulse, means the near approach 
of two celestial bodies to each other 
in angular distance, so as to be seen, 
for instance, within the field of a tel- 
escope. 

Apses, or Apsides, are the two points 
in the orbits of the planets, or satel- 
lites, which at the greatest and least 
distance from the centre of motion. 
And a line joining these two points is 
called the line of the apses. 

Apus, a constellation in the south- 
ern hemisphere, containing eleven 
stars. 

Aquarius, one of the zodiacal con- 
stellations, containing one hundred 
and eight stars. 

Aquila, the eagle, a northern con- 
stellation containing (with Antinous) 
seventy-one stars. 

Ara, the altar, a southern constella- 
tion, containing nine stars. 

Arc, is a part of a curve line, or cir- 
cle ; for example, the latitude and 
declin'ation are arcs of the meridian, 
and longitude is the arc of the equa- 
tor or parallel circle. 

Arc of Direction, is that arc which 
a planet appears to describe when its 
motion is direct or progressive. 

Arc of Retrogradation, is that which 
a planet describes whilst moving con- 
trary to the order of the sign, or from 
east to west. 

Arctic Circle. A small circle sur- 
rounding the north or arctic pole, and 
distant from it 23° 28'; it passes 
through the north pole of the eclip- 
tic ; this and the Antarctic Circle, are 
called Polar Circles. 



ASTRONOMICAL TERMS. 



105 



Jircturus, a star of the first -magni- 
tude in the constellation Bootes. 

Jlrgo jYavis, a southern constella- 
tion, containing sixty-four stars. 

Argument, is an arc given, by which 
another may be found in some pro- 
portion to it. 

Argumerit of Latitude, is an arc of 
the orbit of a planet, intercepted be- 
tween the ascending node, and the 
place of the planet from the sun, ac- 
cording to the order of the signs. 

Aries, the Ram, one of the northern 
constellations of the zodiac ; it con- 
tains sixty-six stars. 

Arietis, a star of the second magni- 
tude, in the head of the Ram. 

Armillary Sphere. A name given 
to an artificial sphere, representing 
the several circles of the system of 
the world. 

Ascending, a term denoting any 
star, degree, or any point of the heav- 
ens, rising above the horizon. 

, Ascending Latitude, is the latitude 
of the moon or planet when going 
northward. 

Ascending A'ode, is that point of a 
planet's orbit, where it cuts the eclip- 
tic in going northward ; it is marked 

a- 

Ascension. See Oblique and Right. 

Ascensional Difference, is the differ- 
ence between the right and oblique 
ascension, or descension ; or it is the 
interval of time the sun rises or sets, 
before or after six o'clock. 

Ascii.aive the inhabitants of the tor- 
rid zone, who at certain times of the 
year have no shadow. 

Aspect, is the situation of the stars 
or planets with respect to each other. 
There are reckoned five aspects, viz. 
Conjunction, d ; Sextile :i(C ; Quartile, 
n ; Trine, /\ ; Opposition, § . 
Acj=0°=Os, a^=60°=2s, ^0=^0° 
=3s a/^=i20°=4=, and §=18G'' 

Astrolabe, signifies a stereographic 
projection of the sphere upon the 
plane of one of the great circles. The 
Sea Astrolabe, is an instrument used 
for the altitude of the sun and stars. 

Astrology, a pretended art of fore- 
telling future events by the aspects 
and positions of the stars. 

Astronomy, from dster, a star, and 
JVomos, a law, is the science by which 
we are taught the motions, magni- 
tudes, distances, &c. of the heavenly 
bodies. 

Astrocope, an astronomical instru- 
ment, invented by W. Shuckhard. 

o 



Atair, a star of the first magnitude, 
in the constellation Aquila. 

Atmosphere, is that elastic invisible 
fluid which surrounds the globe, and 
causes the refraction and twilight. 

Attraction, according to the Newto- 
nian philosophy, is that innate princi- 
ple of matter, by which bodies mutu- 
ally tend towards each other. 

Auriga, the Waggoner, a northern 
constellation containing 66 stars. 

Aurora,\hQ morning twilight. See 
Twilight. 

Aurora Borealis, or JVorthern Lights, 
a kind of meteor of a pale colour, 
sometimes seen in the northern parts 
of the heavens, supposed to be an 
electrical phenomenon. 

Austral, southern. The six signs of 
the zodiac, which are south of the 
equinoctial, are called Austral signs. 

Autumn, the third quarter of the 
year, which begins when the sun en- 
ters Libra, that is, about the 21 st or 
22d of September, when it is equal 
day and night. 

Autumnal Equinox, is the time when 
the sun enters Libra, or the descend- 
ing point of the ecliptic, called also 
the Autumnal point. The signs Libra, 
Scorpio, and Sagittarius, are called 
autumnal signs. 

Axis of the World, is an imaginary 
line passing through the centre of the 
earth, and extending both ways to the 
sphere of the fixed stars, around which 
they appear to perform their diurnal 
revolutions, by the motion of the 
earth upon this axis. 

Axis of the Circles of the Sphere, are 
right lines supposed to be drawn 
through their centres, perpendicular 
to their planes. 

Azimuth, of the celestial bodies, is 
an arc of the horizon intercepted be- 
tween the meridian and a vertical 
circle passing through the body. 

Azimuth Compass, an instrument 
for finding the magnetic azimuth, or 
amplitude of a celestial body. 

B. 

B, in the astronomical tables, stands 
fur Bissextile, or Leap Year. 

Bach Staff, an instrument invented 
by Captain John Davis, a Welchman, 
about the year 1590 ; it was used for 
taking the sun's altitude at sea. 

Barometer, an instrument for show- 
ing the gravity of the atmosphere ; 
it is commonly used for foretelling 
the changes of the weather ; but is 
useful for ascertaining the altitude of 



106 



DICTIONARY OF 



mountains, and for correcting the va- 
riation of the refraction arising from 
the changes in tiie density of the at- 
mosphere. 

Bear, the name of two constellations 
near the north pole. See Ursa Major 
and Minor. 

Beard of a Comet, a.re the rays which 
it emits from its head in the direction 
of its motion, 

Bella.trix, a star of the second mag- 
nitude in the left shoulder of Orion. 

Binocle, or Binocular Telescope, a 
telescope by which the object can be 
viewed with both eyes at the same time. 

Bissextile, or Leap Year, is a year 
consisting of 366 days, which happens 
every fourth year. The reason for 
adding a day every fourth year, is be- 
cause the tropical year exceeds the 
civil year six hours. To find Leap 
Year, divide the year by four, and if 
nothing remains, it is Leap Year. 
For instance, 1818 divided by 4, gives 
the quotient 454, and the remainder 
is two, which shows that the year 1818 
is the second after Bissextile or Leap 
Year, and that 1820 will be Leap 
Year. 

Bootes, a northern constellation, 
containing fifty four stars. 

Boreal Signs, are those on the north 
side of the equinoctial, viz. Aries, 
Taurus, Gemini, Cancer, Leo, and 
Virgo. 



Calendar. See Almanac. There 
are a great many different calendars, 
adapted to the various uses of common 
life, viz. the Roman calendar, the Gre- 
gorian calendar, the Julian, the jRe- 
formed, and the French new calendar, 
&c. 

Cancer, the Crab, one of the con- 
stellations of the zodiac ; when the 
sun enters this sign it has the greatest 
declination northward ; it contains 
eighty-three stars. 

Cards Major, or the Great Dog, is 
a southern constellation, that contains 
Sirius, one of the brightest fixed stars 
in the heavens ; the number of stars 
in this constellation is thirty-one. 

Canis Minor, the Little Dog, a north- 
ern constellation consisting of four- 
teen stars. 

Canopvs, a star of the first magni- 
tude, in the rudder of Argo, the ship ; 
its right ascension is 95° and dec. 
52° 36' south, and therefore is not vis- 
ible in the latitude of London. 

Capella, or the Goat, a bright star 
of the first magnitude, in the left 



shoulder of Auriga ; right ascension 
75° 49', declination 45° 48'. 

Cardiiial Points, are the north, south, 
east, and west points of the horizon. 

Cardinal Signs, are Aries, Cancer, 
Libra, and Capricorn. The begin- 
ning of these signs are in the Cardi- 
nal points of the ecliptic. 

Cassiopeia, a northern constellation, 
consisting of fifty-five stars. 

Castor, the name of a star of the 
first magnitude, in the constellation 
Gemini. 

Catalogue of the Stars, is a table of 
the fixed stars, arranged according to 
their right ascensions, or longitudes, 
with their declinations, or latitudes, 
together with their annual variations 
and magnitudes. 

Cauda Capricorni. See Dineb Al- 
gedi. 

Cauda Ceti. See Dineb Haetos. 

Cauda Cygni. See Dineb Adi- 
gege. 

Cauda Delphini, a star of the third 
magnitude on the tail of the Dolphin, 
marked E. 

Cauda Draconis, the Dragon's tail. 
The moon's descending node. See 
Descending Node. 

Cauda Leonis, sometimes called Lu- 
cida Cauda. See Dineb Eleced. 

Cauda Urse Majoris, a star of the 
third magnitude, near the end of the 
Great Bear's tail, called also Bene- 
nath. 

Cauda Urse Minoris. See Pole Star. 

Centaurzis, one of the southern con- 
stellations, which contains thirty-five 
stars. 

Centrifugal Force, is that force by 
which all bodies moving about a cen- 
tral body, or force, endeavour to fly 
off in tangent lines. 

Centripetal Force, is that by which 
a body moving round another, tends 
towards it; this, and the centrifugal 
force acting upon the planets, cause 
them to describe curvilinear orbits 
about the sun. 

Ceres, or Piazzi, a primary planet 
moving between the orbits of Mars 
and Jupiter ; it was discovered on the 
1st of January, 1801, by M. Piazzi. 

Cettis, the Whale, a southern con- 
stellation, containing ninety-seven 
stars. 

Characters, are certain marks used 
in this science, as abbreviations. The 
astronomical characters are the fol- 
lowing : The tioelve signs of the zo- 
diac, are cp Aries, the Ram ; y Taurus, 
the Bull; n Gemini, the Twins; 
23 Cancer, the Crab ; ^ Leo, the 



ASTRONOMICAL TERMS. 



107 



Lion ; TI^ Virgo, the Virgin ; £1 Libra, 
the Balance; n|. Scorpio, the Scor- 
pion; / Sagittarius, the Archer; 
]ff Capricornus, the Goat ; -is. Aqua- 
rius, the Water bearer ; }{ Pisces, the 
Fishes. The Planets. Q The sun ; 
9 Mercury ; $ Venus ; Earth ; 
^Mars; g Vesta; ^Juno; ^ Ceres; 
$ Pallas; Ij. Jupiter; ]-j Saturn; 
1^ Uranus. The Aspects. c5 Conjunc- 
tion ; ^ Sextile ; n Quartile ; ^Trine ; 
<9 Opposition. The J\''odes. ^ As- 
cending node; ^ Descending node. 
Motion and Time. ° Degree ; ' min- 
ute ; "seconds: hhour; m minute; 
s second ; A. M. Ante Meridian, or 
before noon ; P. M. Post Meridian, or 
afternoon. Sometimes M. is put for 
morning, and A. for afternoon. 

Charles's Wain, seven conspicuous 
stars in Ursa Major, or the Great 
Bear. 

Chronometer, an instrument con- 
trived for the purpose of measuring- 
small portions of time ; or v/atciies 
used for finding the longitude, are 
generally called by this name, or 
Time-keepers. 

Circle, a plane fiajure, bounded by 
a curve, equally distant from a point 
called the centre ; and all lines drawn 
from this point to the circumference, 
are equal. 

Circles of the Sphere, diVe those whose 
planes pass through the sphere, and 
have their circumference upon its 
surface. If the plane pass through 
the centre of the sphere, it is called 
a great circle, if not, it is called a less 
circle. The equator and ecliptic are 
great circles : the polar circles and 
the parallels of latitude or declination, 
are small circles. 

Circles of Altitude. See Vertical 
Circles. 

Circles of Declination, are great cir- 
cles perpendicular to the equinoctial. 

Circle of Illumination, is that im- 
aginary circle which divides the en- 
lightened hemisphere of the earth 
from the darkened. 

Circles of Latitude, or secondaries 
to the ecliptic, are great circles perpen- 
dicular to the ecliptic, and intersect- 
ing in its poles. 

Circles of Longitude. See Longi- 
tude. 

Circles of perpetual Apparition, are 
small circles parallel to the equator, 
and touching the horizon of any giv- 
en place. 

Circles of perpetual Occultation, are 
also small circles parallel to the equa- 
tor, and touching the lower pait of 



the horizon, or never appearing above 
it. 

Circles of Position, are great circles 
of the sphere, passing through the com- 
mon intersection of the meridian and 
horizon, and through any degree of 
the ecliptic, or centre of a star or 
planet. 

Circular Velocity, is the velocity of 
a revolving body, measured by an arc 
of a circle. 

Circumpolar Stars, are such as re- 
volve round the pole, without setting 
in a given latitude. 

Civil Day, the time allotted for day 
in civil purposes ; it begins different- 
ly in different nations ; it is divided 
into twenty-four hours. 

Civil Month, is the same as given in 
the common almanacs. 

Civil Year, is that which is appoint- 
ed by any government, to be used 
within its own dominions. 

Clock, a well known machine for 
measuring time, regulated by the 
uniform motion of a pendulum. Com- 
mon clocks are made to show mean 
solar time, but those used at observa- 
tories, for the purpose of observing 
the time of the stars transiting the 
meridian, show sidereal time. 

Columha JVoashi, Noah's dove, a 
small constellation in the southern 
hemisphere, consisting of ten stars. 

Colurcs, are two great circles, 
which intersect each other at right 
angles, in the poles of the world, di- 
viding the ecliptic into four equal 
parts, denoting the four seasons of the 
year ; the one passing through Aries 
and Libra, is the Equinoctial Colure ; 
and the other, passing through Cancer 
and Capricorn, the Solstitial Colure. 

Coma Berenices, or Berenice's Hair^ 
a northern constellation, consisting of 
forty-three stars. 

Comet, a celestial body, frequently 
called a blazing star, moving in a very 
eccentric orbit, having a vapour-like 
appendage. The comet moves in the 
planetary regions, appearing and dis- 
appearing at very uncertain intervals 
of time. 

■Cometarium, a machine showing 
the motion of a comet about the 
sun. 

Commutation. See Angle of Com- 
mutation. 

Complement of an Arc or an Angle, 
is what it wants of 90° ; thus we say, 
the complement of altitude or coalti- 
tude, wliich is the zenith distance ; 
the complement of latitude or decli- 
nation, which is the polar distance. 



108 



DICTIONARY OF 



Conjunction of two celestial bodies, 
is when they have the same degree 
of longitude. See Apparent and True 
Conjunction. 

Consequentia, in astronomy, is when 
the planets move according to the or- 
der of the signs. 

Constellation, is a number of stars 
contained within some assumed fig- 
ure, as a Lion, an Eagle, a Bear, &c. 

Cor Caj-oli,a,n extra constellated star 
of the second magnitude, its right as- 
cension and declination at the begin- 
ning of 1818, was right ascension 
191° 52^' declination 39° 18^' N. 

Cor Hydrce, the heart of Hydra. A 
star of the second magnitude in the 
constellation Hydra. 

Cor Leonis, or Regulus. A star of 
the first magnitude in the constella- 
tion Leo. 
Cor Scorpionis. See Antares. 
Corona Borealis, the Northern Crown, 
a constellation containing 21 stars. 

Corona Meridionalis, the Southern 
Crown. This constellation contains 
12 stars. 

Corvus, the Raven, a constellation 
in the southern hemisphere, contain- 
ing nine stars. 

CosmicalRising and Setting, \s when a 
star rises or sets at the time of sunrise. 

Cosmography, a description of the 
world, showing the structure of the 
heavens, with the disposition of the 
stars, and parts of the earth. 

Crater, the Cup, a southern constel- 
lation consisting of thirty-one stars. 

Crepesculum. See Twilight. 

Culmination, the transit or passage 
of a star over the meridian. 

Curtate Distance of a planet from the 
earth or sun, is the distance of the 
earth or sun from that point where 
a perpendicular passing the planet 
cuts the ecliptic. 

Cycle, a certain period of time, in 
which the same revolutions begin 
again, a periodical space of time. 

Cycle of Indictisn, or Roman Indic- 
tion. This cycle has no connection 
with the celestial motions ; it is a 
period of 15 years. To find this cycle, 
add three to the given year, and di- 
vide the sum by fifteen, and what re- 
mains is the indiction. 

Cycle of the moon, or the Lunar Cy- 
cle, is a period of nineteen years, in 
which the new and full moons return 
on the same days as they did jiine- 
teen years before ; this cycle is called 
the Golden JVumber, for the finding of 
which, see Golden Nuniher. 

Cycle of the Sun, is a period of 28 



years, in which time the days of the 
month return again to the same days 
of the week, &c. See Solar Cy- 
cle, 

Cygnus, the Sican, a constellation 
of the northern hemisphere, contain- 
ing eighty-one stars. 

D. 

Day, is that portion of time from 
the appearance of the sun, to its dis- 
appearance ; this is called an artificial 
day. 

Day, Astronomical. The Astronom- 
ical day begins at apparent noon, and 
is counted twenty-four hours to the 
following noon. 

Day, Civil. See Civil day. 

Day, Natural ; the natural day is 
either Astronomical or Civil. See 
these articles. 

Day, Siderial. See Siderial day. 

Dechotomized. See Quadratures. 

Declination, is the distance of the 
sun, moon, or stars from the equinoc- 
tial, either north or south. 

Declination Circles, or Circles of 
Declination, are great circles perpen- 
dicular to the equinoctial, and passing 
through its poles. 

Degree, the 360th part of a circle, 
or the 30th part of a sign. 

Delphinus, the Dolphin, a northern 
constellation, containing 18 stars. 

Deneb, the Arabic term for tail ; the 
name of several fixed stars. See Cor. 

Depression of the Poles, is to ad- 
vance towards the equator. 

Depression of the Sun or Star, is 
its vertical distance below the horizon. 

Descending Node, is that point of a 
planet's orbit, where it cuts the eclip- 
tic, proceeding southward, marked y. 

Descension. See Oblique and Right. 

Dial. An instrument to show the 
hour of the day by the sun. 

Digit, the twelfth part of the sun 
or 'moon's diameter, and is used to 
show the degree of obscuration in an 
eclipse. 

Direct. See Consequentia. 

Disc, is the face of the sun, or moon, 
as it appears to the eye. 

Disc of the Earth, is the difference 
between the horizontal parallax of the 
sun and moon ; and is used in the 
construction of solar eclipses. 

Distance of the Sun, Moon, and Plan- 
ets, is the real distances of any of 
these as found by their parallaxes. 

i)mrna/,of or belonging to the day. 

Diurnal Arc, is the arc described 
by the celestial bodies from their ris- 
ing to their setting. 



ASTRONOMICAL TERMS. 



109 



■ Diurnal Motion, is the degrees, 
minutes, or seconds, a celestial body 
describes in twenty- four hours. 

Diurnal Motion of the Earth, is its 
rotation on its axis. 

Dog. See Canis Major and Canis 
Minor. 

Dominical Letter, one of the first 
seven letters of the alphabet, where- 
with the Sundays are marked in the 
almanacs with a red letter throughout 
the year. To find the Sunday letter 
for any year, for instance, 1820; 
20X^4^X2=27, this -f- by 7=3 six- 
sevenths, and 7 — 6=1, which is A ; 
as 1820 is leap year, this will be the 
Sunday letter from the end of Febru- 
ary, to the end of the year ; but from 
the beginning of the year to the end 
of February, the dominical will be B, 
so that the Sunday letters for 1820, 
are B and A. 

Draco, the Dragon, a northern con- 
stellation, containing, or consisting 
of, eighty stars. 

Dubhe, or a Ursa Major, a star be- 
tween the first and second magnitude, 
the most northern of the pointers. 

E. 

Earth, or Terra, one of the planets ; 
its orbit lies between Venus and Mars. 
Its diameter is 7914 miles, and obser- 
vation proves it to be inhabited. 

East, one of the cardinal points, be- 
ing that on which the sun rises at 
equinoxes. 

Eclipse, a privation of light of the 
sun or moon, by the interposition of 
some opaque body. 

Ecliptic, Q.gxea.i circle of the sphere, 
or orbit of the earth ; it is inclined to 
the equator, or equinoctial, at an angle 
of about 23° 28'. The sun appears to 
describe this circle in the heavens 
every year. 

Elements, in Astronomy, are those 
principles deduced from observation, 
by which tables of the planetary mo- 
tions are computed. 

Elevation of the -pole or star, is the 
height of the pole or stars in degrees 
above the horizon. 

Elongation. See Angle of Elonga- 
tion. 

Emersion, is the reappearance of 
a celestial body after having been 
eclipsed ; when a satellite reappears 
after having been eclipsed by the 
shadow of the planet, it is called the 
emersion. 

Epact. See Annual and Menstrual 
Epacts. 



Ephemeris, tables containing the 
computations of the places of the 
heavenly bodies for every day at noon. 

Epoch, the same as Era, which see. 

Equation of the Centre. See An- 
nual Equation. 

Equation of the Moon's mean Mo- 
tion, depends upon the situation of 
the moon's apogee and nodes with re- 
spect to the sun. 

Equation of Time, is the difference 
between apparent and mean time, or 
between the sun's mean motion and 
right ascension. 

Equatoral, a Very useful instrument 
in Astronomy, for taking the altitude, 
azimuth, right ascension, &c. of the 
heavenly bodies. 

Equinoctial, in the heavens, or equa- 
tor on the earth, is one of the great 
circles of the sphere, whose poles are 
the poles of the world. 

Equinoctial Colures. See Colures. 

Equinoctial Points, Z-xe Aries and Li- 
hra, and when the sun enters either of 
these points it is called the equinox. 

Era, or Epoch, means a fixed point 
of time from which to begin the com- 
putation of the ensuing years. 

Eridanus,the river, a southern con- 
stellation, consisting of eightj-four 
stars. 

Evection. See Angle of Evection. 

Eccentric. See Annual Equation, 
and Anomaly. 

Eccentricity, is the distance of the 
centre from the foci of the elliptical 
orbit of the planet. 

F. 

Fac2ilc, are certain bright spots, fre- 
quently seen upon the disc of the sun. 

Falcated. The moon or a planet is 
said to be falcated, when the enlight- 
ened part appears of a crescent form 
like the Moon or Venus, when near 
the sun. 

Fixed Signs of the Zodiac, are Tau- 
rus, Leo, Scorpio, and Aquarius ; they 
are so called because the season is 
considered to be more settled when 
the sun passes through these signs, 
than at any other times of the year. 

Fixed Stars, are such*as do not ap- 
pear to change their relative situa- 
tions. They are properly called stars, 
in contradistinction to planets and 
comets. 

Fomahaut, a fixed star of the first 
magnitude, in the mouth of the south- 
ern fish. 

Fore Staff, an instrument used at 
sea for raking the altitudes of the ce- 
lestial bodies. It is now superseded 



no 



DICTIONARY OF 



by the use of more perfect instru- 
ments. 

G. 

Galaxy, is that whitish track which 
appears to encompass the heavens ; 
it is very visible of a bright night, 
when the moon is absent. Dr. Her- 
schel found it to consist of innu- 
merable small stars and nebulous 
matter. 

Gemma, a, Corona Borealis, or Al- 
pkacea, a star of the second magnitude 
in the Northern Crown. 

Gemini, a zodiacal constellation in 
the northern hemisphere, containing 
eighty-five stars. 

Geocentric Place of a planet, is its 
place as seen from the earth. 

Geocentric Latitude of a planet, is 
its perpendicular distance from the 
ecliptic as seen from the earth. 

Geocentric Longitude of a planet, is 
its elliptical distance from the first 
point of Aries, as seen from the earth. 

Gibbous, is a term used for the fig- 
ure of the enlightened parts of the 
moon, from the time of the first quar- 
ter to the full, and from that of the 
full to the last quarter. 

Gnomon, an apparatus used by the 
ancients for finding the altitudes and 
declinations of the celestial bodies. 

Golden JVumber, or Cycle of the 
Moon, which see. To find the Golden 
Number for any year, for example, 
1819 : First, 181941=18^0 ; this di- 
vided by 19, gives 95, and 15 for the 
remainder, which is the Golden Num- 
ber, as required. 

Gravitation, or Gravity. See At- 
traction. 

Great Bear, a northern constella- 
tion. See Ursa Major. 

Great Circles. See Circles of the 
Sphere. 

Gregorian Calendar, is the reformed 
calendar now in use, which takes its 
name from Pope Gregory the Xlllth. 

Gregorian Epoch, is the time when 
the Gregorian computation first took 
place, which was in the year 1582. 

Gregorian Telescope, is a reflecting 
telescope, halving a hole in the centre 
of the great speculum, through which 
the image is thrown by the small re- 
flector to the eye. The distinctness 
of the object seen through this tele- 
scope is somewhat diminished by the 
liole in the great speculum. 

Gregorian Year, the year now in 
use, called the new style ; it consists 
of 3G5 days for three years, and 366 
every fourth year, the same as the 
Julian account ; but as this exceeds 



the tropical year by about eleven 
minutes and one twentieth, and which 
in Pope Gregory's time amounted to 
ten days, he ordered so many days to 
be struck out of the calendar ; and to 
prevent the like anticipation in fu- 
ture, it was ordered that every cen- 
tury not divisible by four, to be reck- 
oned common years, v/hich in the Ju- 
lian account are bissextile. 

H. 

Halo, a very conspicuous circle of 
about 45 degrees in diameter, sur- 
rounding the sun or moon, supposed 
to arise from the refraction of light in 
passing through the thin vapours of 
the atmosphere ; they are most com- 
monly visible in stormy weather. 

Heaven, is the infinite expanse in 
v/hich the stars, planets, and comets, 
are situated, or perform their respec- 
tive revolutions. 

Heliacal rising and setting of a Star, 
is, properly, when it rises or sets with 
the sun. Or a star is said to rise heli- 
acally when it is first seen after con- 
junction with the sun, and to set heli- 
acally when it is so near the sun as 
to be hid by his beams. 

Heliocentric -place of a planet, is its 
latitude and longitude, or place in 
the heavens, as seen from the sun. 
The heliocentric motion of a planet is 
always direct, the sun being its cen- 
tre of motion. 

Heliometer, a kind of micrometer for 
measuring the diameter of the sun, 
moon, and stars. 

Hemisphere, is the half of a globe 
or sphere divided by a plane passing 
through its centre. The equator or 
equinoctial divides the sphere into 
two equal parts, called the northern 
and southern hemispheres. 

Hercules, a northern constellation, 
containing one hundred and thirteen 
stars. 

Heterocii,a.ve the inhabitants of the 
two temperate zones, whose shadows 
at noon are always projected the same 
way with regard to themselves, or al- 
ways contrary ways with respect to 
each other. 

Horizon, is a great circle of the 
spliere, dividing the heaven and the 
earth into two equal parts, called the 
upper and lower hemisphere. See 
Apparent. 

Horizontal, something relating to, 
or parallel to the horizon. 

Horizontal Parallax, is the parallax 
of a celestial body, when in the hori- 
zon. See Parallax. 



ASTRONOMICAL TERMS. 



Ill 



Hour, is the 24th part of a natural 
day, answering to ]5° of the equator. 

7/?/(Zra, a constellation of the south- 
ern hemisphere, containing (JO stars. 

I. 

Immersion, in an eclipse, is the be- 
ginning ; the term is frequently used 
in reference to Jupiter's satellites ; 
when the satellite enters the shadow 
of the planet, it is called the immer- 
sion. When a star or planet is so 
near the sun that it cannot be seen, it 
is called an immersion. 

Inclination of the orbit of a planet, 
is the angle which the plane of the 
planet's orbit makes with the plane 
of the ecliptic, or earth's orbit. 

Indiction. See Cycle of Indiction. 

Informed Stars, are such as were 
formerly not included in constella- 
tions ; but modern astronomers have 
contrived to include all the unformed 
stars. 

Ingress, is the sun's entering any 
of the twelve signs, or other parts of 
the ecliptic. 

Julian Year, is the year establised 
by Julius Caesar, now called the old 
style. See Gregorian Year. 

Juno, or Harding Planet, one of 
the newly discovered planets, and 
the sixth in order from the sun ; it 
was first discovered in 1804. 

Jupiter, one of the superior planets, 
the largest in the solar system ; its 
diameter is 91,000 miles. 



Latitude, in geography, is the height 
of the pole ; or it is an arc of the me- 
ridian, intercepted between the zenith 
and the equator, and is north or south, 
according as the place is on the north 
or south side of the equator. 

Latitude of the Moon, is her perpen- 
dicular distance from the plane of the 
ecliptic ; and it is north latitude, when 
she is on the north side of the eclip- 
tic, and south latitude when on the 
south side. It is north ascending, from 
the ascending node, to her northern 
limit ; and north descending , from the 
northern limit to the descending node. 
It is south ascending, from her south- 
ern limit to the ascending node ; and 
south descending, from the descending- 
node to her southern limit. And the 
like is to be understood of the planets. 

Leap Year. See Bissextile. 

Leo, the Lion, a northern and zoda- 
ical constellation, containing ninety- 
five stars. 



Leo Minor, or Little Lion, a modern 
constellation, in the northern hemis- 
phere, containing fifty-three stars. 

Lejms, the Hare, a southern con- 
stellation, containing nineteen stars. 

Libra, the Balance, or Scales, a zo- 
daical constellation, containing fifty- 
one stars. 

Librations of the Moon, are periodi- 
cal irregularities in her motion, by 
which the same face is not always 
turned towards the earth. 

Limit of a Planet, signifies its great- 
est heliocentric latitude. 

Longitude of a celestial Body, is the 
distance of that point of the ecliptic, 
cut by a secondary to it, passing 
through the body from the beginning 
of Areis. 

Lunar Distance, is a term used in 
nautical astronomy, for the distance 
of the moon from the sun, or fixed 
stars ; the measurement of which, 
whereby the true distance can be 
computed, is found to be of the great- 
est use in determining the longitude. 

Lupus, the Wolf, a constellation in 
the southern hemisphere, containing 
twenty-four stars. 

Lynx, a modern constellation in the 
northern hemisphere, of forty-four 
stars. 

Lijra, the Harp, a northern constel- 
lation, containing twenty-one stars. 

M. 

MaculcB, are dark spots that are fre- 
quently seen upon the disc of the sun. 

Magnitudes. The fixed stars, ac- 
cording to their size or brightness, 
are divided into magnitudes ; the 
brightest are called stars of the first 
magnitude ; the next in brightness, 
stars of the second magnitude ; and 
so on to the sixth or seventh magni- 
tudes, which are the smallest that can 
be seen with the naked eye. 

Mar cab, or » Pegasus, a fixed star 
of the second magnitude, near the 
wing of Pegasus. 

Mars, a superior planet, and fourth 
in order from the sun. 

Mean Anomaly of a planet, is its 
angular distance from the aphelion 
or perihelion, supposing it to revolve 
in a circle with its mean velocity. 

Mean Conjunction of the Sun and 
Moon, is the conjunction of their 
mean longitudes. 

Mean Distance of a planet, is the 
semi-transverse diameter of its orbit. 

Mcnhnar, or cc Cctus, a star of the 
second magnitude, in the head of tlie 
Whale. 



112 



DICTIONARY OF 



Mercury, an inferior planet, the 
nearest to the sun. 

Meridian, a great circle of the 
sphere, passing through the poles of 
the world. 

Micrometer, is an instrument fitted 
to a telescope, for the purpose of 
measuring small angles, such as the 
diameters of the celestial bodies. 

Mid- Heaven, called also Medium 
Ccdi, is that point or degree of the 
ecliptic, which is upon the meridian 
at any time. 

Milky Way. See Galaxy. 

Minute, the 60th part of a degree, or 
of an hour. 

Mirach, or li, Androineda, a star of 
the second magnitude, in the constel- 
lation Andromeda. 

Monoceros or the Unicorn, a north- 
ern constellation, consisting of thirty- 
one stars. 

Month, the 12th part of a year. A 
hc7iar month is the time the moon 
takes to describe the whole circle of 
the ecliptic, and is 27d 7h 43m. A 
synodic month, is the time between 
two conjunctions of the sun and moon, 
and is 29d 12h 44ni 3*. A solar month 
is the mean time of the sun's passing 
through one entire sign of the ecliptic, 
which is about 30d lU^i 29m. 

Moon, the satellite of Terra, and 
which is nearest to the earth of all the 
heiivenly bodies. 

Mutual Aspects, are such as the 
primary planets make among them- 
selves, 

N. 

jXadir, is that point in the heavens 
directly under our feet. 

JVapoleoji, a name given to the con- 
stellation Orion. 

JYcb2ilcB, is a term applied to those 
telescopic stars that have a cloudy ap- 
pearance. 

JVocturnal Arc, is that arc described 
by a celestial body during the night. 

JVodes, are the two opposite points 
where a planet's orbit cuts the eclip- 
tic. 

Nonagisimal Degree, is the highest 
point of the ecliptic above the horizon, 
and is equal to the angle which the 
ecliptic makes with the horizon. It is 
of great use in calculation of eclipses. 

JVorth, one of the cardinal points on 
the compass ; that opposite the south. 

Number of DircMion, is a number 
not exceeding thirty-five, which num- 
ber is the limit of Easter day, always 
falling between the 21st of March and 
25th of April. 



JVutation of the Earth's Axis, is a 
kind of vibratory motion, by which its 
inclination to the plane of the ecliptic 
is subject to a small variation. 

O. 

Oblique Ascension, is that point of 
the equinoctial which rises with a ce- 
lestial body in an obUque sphere. 

Oblique Descension, is that point of 
the equinoctial which sets with a ce- 
lestial body in an oblique sphere. 

Oblique Sphere, is that position of 
the sphere in which the equator and 
its parallels cut the horizon obliquely. 

Observatory , a place or building fit- 
ted up with proper instruments for ob- 
serving the celestial bodies. 

Occidental, westerly. A planet is 
said to be Occident when it sets after 
the sun. 

Occultation, is the obscuration of a 
star or planet by the interposition of 
the moon. 

Opposition, is that aspect of the ce- 
lestial bodies when they are 180° from 
each other. 

Orbus Magnus, a term formerly used 
to signify the orbit of the earth. 

Orbit, is the curvilinear tract in 
which the planets perform their re- 
spective revolutions round the sun. 

Oriental, easterly. A planet is said 
to be oriental, when it rises before the 
sun. 

Orion, a constellation situated upon 
the equinoctial, containing seventy- 
eight stars. 

Orrery, a machine for exhibiting the 
various motions of the planetary bodies. 
It is more properly called a Planeta- 
rium. 

Ortive Amplitude, is the eastern am- 
plitude of a heavenly body. 

P. 

Pallas, ov Olbers, one of the newly- 
discovered planets, and the eighth in 
order from the sun. 

Parallax, is the angle formed at the 
centre of a star by two lines, one 
drawn from the centre, and the other 
from the surface of the earth. 

Parallax, in altitude, is the differ- 
ence between the true and apparent 
altitude of the body ; or the difference 
between the altitude at the surface and 
centre of the earth. 

Parallax Horizontal. See Hori- 
zontal Parallax. As the altitude of a 
body is affected by parallax, so is its 
right ascension, declination, latitude, 
and longitude. 



FIRST BOOK IN ASTRONOMY. 



113 



Parallel Sphere, is that position of 
the sphere in which the equator is 
parallel to the horizon. 

Parallels of Mlitude, are small cir- 
cles parallel to the horizon. 

Parallels of Declination, or Paral- 
lels of Latitude, are small circles par- 
allel to the equinoctial or equator. 

Parhelion, a mock sun. 

Pegasus, a northern constellation, 
containing eighty-nine stars. 

Penumbra, is a faint shade surround- 
ing the perfect shadow, in an eclipse. 

Perigee, is that point of the moon's 
orbit which is nearest to the earth. 

Perihelion, is that point of a planet's 
orbit which is nearest to the sun. 

Periceci, are those who live under 
the same parallel of latitude, whether 
north or south, but on opposite meridians. 

Periscii, are the inhabitants (if any) 
that live within the polar circles. 

Perseus, a northern constellation, 
containing fifty-nine stars. 

Phases, are the different appear- 
ances of the enlightened parts of the 
Moon, Venus, and Mercury. 

Phenomenon, any singular appear- 
ance in the heavens, as an eclipse, 
comet, &c. 

Phcenix, a southern constellation, 
containing thirteen stars. 

Pisces, the last of the zodiacal signs, 
which contains 113 stars. 

Place of a Celestial Body, is simply 
its situation in the heavens, and is usu- 
allj'' expressed by its latitude and lon- 
gitude. 

Planet^ is a celestial body revolving 
about the sun. The planets may be 
known from the fixed stars, by their 
change of situation in the heavens. 

Pleiades, or Seven Stars, a cluster 
of stars on the neck of the Bull. 

Poles, are the extremities of the 
axis of the world ; one called the north, 
and the other the south pole. 

Pollux, one of the twins, also the 
name of a star of the second magnitude, 
in the constellation Gemini. 

Precession of the Equinoxes. This 
is a very slow motion of the equinoc- 
tial points in antecedentia or from east 
to west ; this motion is about 50" in a 
year. 

Primary Planets, are those that 
have the sun for their centre of motion. 

Procyon, or ec Canis Minor, a star 
of the first magnitude in the constella- 
tioa Canis Minor. 

Q. 

Quadrant, ihe fourth part of a circle, 
or 90°. Also an instrument, variously 



constructed, for the purpose of taking 
the altitude and angular distances of the 
heavenly bodies. 

Quadrature, is that position of the 
moon when she is 90 degrees from the 
sun. 

Quartile, Aspect. See Aspect. 
R. 

Radius Vector, is that imaginary 
line connecting the planet and sun, and 
which, as the planet moves round the 
sun, describes equal areas in equal 
times. 

Reduction, is the difference between 
the planet's orbit, place, or argument 
of latitude, and ecliptic place. 

Ras-algethi, ^ Hercules. 

Ras-alhague, en. Ophinchus. 

Rastaban, y Draco. 

Refraction, is the bending of the 
rays of light, in passing through the at- 
mosphere, thereby causing the heav- 
enly bodies to be more elevated above 
the horizon, than thej'' really are. 

Regulus. See Cor Leonis. 

Reticula, an instrument invented for 
ascertaining the quantity of an eclipse. 

Retrograde. See Antecedentia. 

Revolution, is the period of any ce- 
lestial body. 

Rigel, a star of the first magnitude, 
on the left foot of Orion. 

Right Ascension, is that point of the 
equinoctial which comes to the merid- 
ian with any celestial body, and is 
reckoned from the first point of Aries. 
The degree of the equinoctial, that rises 
with any celestial body in a right 
sphere, is called its right ascension, 
and the degree of the equator which 
sets with any celestial body in the said 
sphere, is called its right descensionv> 

Right Sphere, is that on which the 
equator and its parallels, cut the hori- 
zon at right angles. 

Rising of a Celestial Body, is its 
appearance above the eastern horizon. 

Rotation. SeeRevolution. 
S. 

Sagitta, the Arrow, a northern con- 
stellation, containing eighteen stars. 

Sagittarius, the Archer, one of the 
zodiacal constellations,containing sixty- 
nine stars. 

Saros, called also the Chaldean 
Saros, is a period of 223 lunations, in 
which the same eclipse returns again, 
within an hour or two, but not with 
the same degree of obscuration. 

Satellites, or Secondary Planets, 
are those celestial bodies that revolve 
round some primary planet ; the moon, 
is a secondary planet, as are those small 



114 



DICTIONARY OF 



stars that accompany Jupiter, Saturn, 
and Herschel. 

Saturn, one of the superior planets, 
and was formerly considered the most 
distant in the solar system ; it is the 
tenth in order from the sun. 

ScJieat, or /3 Pegasus, a star of the 
second magnitude, in the constellation 
Pegasus. 

Scorpio, the Scorpion, a zodiacal 
constellation, containing 44 stars. 

Seasons, are the four quarters of the 
year, viz. Spring, Summer, Autumn, 
and Winter. The first quarter begins 
when the sun enters Aries ; the second, 
begins when the sun enters Cancer ; 
the third, when he enters Libra ; and 
and the 4th, when he enters Capricorn. 

Second, the 60th part of a minute, 
either of time or of motion. 
' Secondary Circles, or Secondaries, 
are all those circles which intersect one 
of the six great circles of the sphere, 
at right angles. 

Secondary Planets. See Satellites. 

Serpens, a northern constellation, 
called the Serpent of Ophinchus ; it 
contains sixty-four stars. 

Serpentarius, a northern constella- 
tion, containing seventy-four stars. 

Setting, is the going down, or disap- 
pearance of a ceTestial body, in the 
western horizon. 

Sextant, the sixth part of a circle ; 
or the name of an astronomical instru- 
ment, used for the same purpose as a 
quadrant. 

Sextile, Aspect. See Aspect. 

Sidereal day, is the time in which a 
star appears to revolve from any me- 
ridian to the same again, which is equal 
tcvthe time of the earth's performing 
one entire revolution upon its axis, 
23h 56ra 4-ls, of mean solar time. 

Sidereal Year, is the time in which 
the earth or sun makes one complete 
revolution in its orbit : that is, from any 
given star to the same again. 

Sign, is the 12th part of the zodiac, 
or ecliptic, which contains 30 degrees. 

Sirius, the Dog- Star, one of the 
brightest stars in the heavens ; in the 
constellation Canis Major. 

Solar Year, is of two kinds, Tropical 
and Sidereal, which see. 

Solstices, is the time when the sun 
enters the tropical points. Cancer and 
Capricorn. 

Solstitial Points, are Cancer and 
Capricorn. 

South, one of the four cardinal points 
of the compass ; when the sun is on 
the meridian, in northern latitudes, it 
is then directly south. 



Sphere, Armillary. See Armillary 
Sphere, Oblique, and Right Sphere. 

Spica, a star of the first magnitude, 
in the constellation Virgo. 

Stars. See Planet and Fixed Stars. 

Stationary. A planet is said to.be 
stationary, when it appears to have no 
motion among the fixed stars. 

Summer. See Seasons. 

Sun, or Sol, the great and central 
luminary of the planetary system. 

Syzygy, means either the conjunc- 
tion or opposition of a planet with the 
sun. 

T. 

Taurus, the Bull, a zodiacal sign, 
containing 141 stars. 

Telescope, a most useful optical in- 
strument, of which there are two kinds, 
the reflecting and refracting, the latter 
of which is best for observing the heav- 
enly bodies. 

Telescopical Stars, are those stars 
which are not visible to the naked eye, 
and can be only seen with a teles- 
cope. 

Terminator. See Circle of Illumi- 
nation. 

Thermometet , an instrument show- 
ing the degrees of heat and cold. It 
is used conjointly with the barometer, 
for correcting the variation in the re- 
fraction, from the change of tempera- 
ture and specific gravity of the atmos- 
phere. 

Tides, the periodical flux and reflux 
of the waters of the sea, supposed to 
be caused by the action of the sun and 
moon upon the ocean. 

Time, is a certain measure of dura- 
tion, depending upon the motion of 
the heavenly bodies. 

Transit, is the passing of a planet, 
just before or over the disc of another 
star or planet, as the passing of Mer- 
cury or Venus over the sun's disc, is 
called a transit ; the same is said of a 
planet or star when it passes the me- 
ridian. 

Tropics, are two lesser circles of the 
sphere parallel to the equinoctial, and 
23° 28' distant from it, being the limits 
of the sun's greatest declination north 
and south. 

True Place of a Planet. See He- 
liocentric Place. 

Twilight, is that partial light which 
is observed in the morning before sun- 
rise, and in the evening, for a short 
time after he is set, which is caused 
by the refraction and reflection of the 
rays of light in passing through the at 
mosphere. 



ASTRONOMICAL TERMS. 



115 



V. 

Vector. See Radius Vector. 

Vega, or Lyra, a star of the first 
magnitude ia the Harp. 

Venus, one of the inferior planets, 
and at times appears the brightest star 
in the heavens. 

Vertex, is that point in the heavens 
directly over our heads, called the ze- 
nith. 

Vertical Circle, is a great circle per- 
pendicular to the horizon, and passing 
through the zenith, and nadir of any 
place. 

Vesta, one of the newly discovered 
planets, and the fifth in order from the 
sun. 

Via Lactea. See Galaxy. 

Vindemiatrix, a star of the third 
magnitude in the constellation Virgo. 

Virgo, a zodiacal constellation, con- 
taining 110 stars. 

U. 

Umbra, the total shadow of the 
earth, moon, and planets. 

Unicorn. See Monoceros. 

Uranus, or the Herschel Planet, a 
superior planet, and the most remote 
in the solar system. 



Ursa Major, the Great Bear, a 
northern constellation, consisting of 
eighty-seven stars. 

Ursa Minor, the Little Bear, a 
constellation near the north pole, which 
contains twenty-four stars, one of which 
is called the pole star. 
W. 

Week, a division of time consisting 
of seven days. 

X. 

Xiphias, the Sword Fish, a southern 
constellation, containing six stars. 
Y. 

Year. See Sidereal, and Solar, Sec. 
Z. 

Zenith. See Vertex. 

Zodiac, a belt or girdle surrounding 
the heavens, in the middle of which 
runs the ecliptic ; it is about 18 degrees 
in breadth. 

Zones, are five large divisions of the 
globe, viz. the Torrid, two Temperate, 
and two Frigid Zones. 

Zubenelg, or B Libra, a star of the 
second magnitude in the constellation 
Libra. 

Zubenesch, or a Libra, a star of the 
second magnitude in Libra, right as- 
cension 22(3° 10', declination 15° 16' S. 



Besides the terms commonly used in Astronomy, this Glossary contains all 
the constellations with the number of stars in each, from Mr. Flarastead's cat- 
alogue ; likewise the names of the most noted stars, with their situations in the 
heavens. To render this glossary as complete as possible, the names of differ- 
ent astronomical instruments are also introduced ; and although the explanations 
of the different articles are but short, yet they will be found sufficient to give 
the learner a just idea of the term he seeks. 



DIRECTION TO THE BINDER FOR THE PLATES. 



Plate I, To face the Title Page. • 
„ II, To face page 6. 
„ III, IV, V, VI, VII, and VIII, to be placed in their order, 

at the end of the book ; and each one to face towards 

the left hand. 



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